Follistatin in treating duchenne muscular dystrophy

ABSTRACT

The present invention provides, among other things, methods and compositions for treating muscular dystrophy, in particular, Duchenne muscular dystrophy (DMD). In some embodiments, a method according to the present invention includes administering to an individual who is suffering from or susceptible to DMD an effective amount of a recombinant follistatin protein such that at least one symptom or feature of DMD is reduced in intensity, severity, or frequency, or has delayed onset.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application filed under 35U.S.C. § 371 based on International Application No. PCT/US2014/012996,filed Jan. 24, 2014, which claims priority to U.S. provisional patentapplication Ser. No. 61/756,996, filed Jan. 25, 2013, and U.S.provisional patent application Ser. No. 61/915,733, filed Dec. 13, 2013,the disclosures of each of which are hereby incorporated in theirentirety.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has beensubmitted electronically in ASCII format and is hereby incorporated byreference in its entirety. The ASCII copy, created on Sep. 11, 2015, isnamed “2015-09-11_2006685-0906_SL.txt” and is 52,305 bytes in size.

BACKGROUND

Duchenne muscular dystrophy (DMD) is a recessive X-linked form ofmuscular dystrophy, which results in muscle degeneration and eventualdeath. The disorder is caused by a mutation in the dystrophin gene,located on the human X chromosome, which codes for the proteindystrophin, an important structural component within muscle tissue thatprovides structural stability to the dystroglycan complex (DGC) of thecell membrane. Dystrophin links the internal cytoplasmic actin filamentnetwork and extracellular matrix, providing physical strength to musclefibers. Accordingly, alteration or absence of dystrophin results inabnormal sarcolemmal membrane function. While persons of both sexes cancarry the mutation, boys typically have a severe phenotype with earlydisability and mortality, whereas females carrying a mutation typicallyexhibit a much milder phenotype.

Presently, there is no known cure for DMD. Many therapeutic avenues havebeen investigated including gene therapy and various administrationprotocols of corticosteroids. While some of these treatments may delaycertain signs and symptoms, there is presently no satisfactorytherapeutic option for DMD patients.

SUMMARY OF THE INVENTION

The present invention provides, among other things, improved methods andcompositions for treating muscular dystrophy, in particular, Duchennemuscular dystrophy (DMD) and/or Becker Muscular Dystrophy, based onfollistatin protein therapy. As described herein, including in theExamples below, the present inventors demonstrated, for the first time,that systemic administration of a recombinant follistatin protein (e.g.,a follistatin-Fc recombinant fusion protein) into a DMD animal modelresulted in effective muscle growth in various tissues throughout thebody and reduced muscle fibrosis and/or necrosis, characteristicsymptoms of DMD. In addition, the present inventors have alsodemonstrated that follistatin-Fc fusion proteins according to thepresent invention have extended serum half-life of up to about 5 days.Without wishing to be bound by any theory, it is contemplated that theunexpectedly long serum half-life may have contributed to the superiorin vivo efficacy. Indeed, prior to the present invention, follistatinwas known to be a modulator of myostatin and activin, both of which areimportant negative regulators of muscle growth. However, prior to thepresent invention, it was reported that follistatin has a particularlyshort serum half-life, which constituted a significant hurdle fordeveloping follistatin as a protein therapeutic. For example, a typicalcommercially available wild-type follistatin (FS315) protein has a serumhalf-life of about an hour. Fc-fusion protein had been used to extendthe serum half-life of follistatin. However, due to the large size ofthe Fc domain and the relatively smaller size of the follistatinprotein, it was thought that a direct fusion of the Fc domain to thefollistatin protein may interfere with the normal structure and functionof a wild-type follistatin protein. The reported poorpharmacokinetic/pharmacodynamic (PK/PD) properties of follistatin anduncertainty associated with follistatin-Fc fusion protein haddiscouraged scientists and clinicians from further developingfollistatin as a protein therapy for DMD or other muscular dystrophy.Indeed, prior to the present invention, gene therapy has been the focusof follistatin based therapy for DMD. The unexpectedly superior in vivoefficacy and half-life shown by the present inventors establishes forthe first time that follistatin can be an effective protein therapeuticfor treatment of DMD.

In one aspect, the present invention provides methods of treatingDuchenne Muscular Dystrophy (DMD) including administering to anindividual who is suffering from or susceptible to DMD an effectiveamount of a recombinant follistatin protein such that at least onesymptom or feature of DMD is reduced in intensity, severity, orfrequency, or has delayed onset. In some embodiments, at least onesymptom or feature of DMD is selected from the group consisting ofmuscle wasting, muscle weakness, muscle fragility, joint contracture,skeletal deformation, fatty infiltration of muscle, replacement ofmuscle with non-contractile tissue (e.g., muscle fibrosis), musclenecrosis, cardiomyopathy, impaired swallowing, impaired bowel andbladder function, muscle ischemia, cognitive impairment function (e.g.,learning difficulties, higher risk of neurobehavioral disorders,cognitive defects), behavioral dysfunction, socialization impairment,scoliosis, and impaired respiratory function.

In some embodiments, a recombinant follistatin protein suitable for thepresent invention includes an amino acid sequence at least 50% (e.g., atleast 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%,or 100%) identical to the wild-type human Follistatin protein

(SEQ ID NO: 1) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEED EDQDYSFPISSILEW.

In some embodiments, the recombinant follistatin protein includes anamino acid sequence at least 70% identical to the wild-type humanFollistatin protein SEQ ID NO:1. In some embodiments, the recombinantfollistatin protein includes an amino acid sequence at least 80%identical to the wild-type human Follistatin protein SEQ ID NO:1. Insome embodiments, the recombinant follistatin protein includes an aminoacid sequence at least 90% identical to the wild-type human Follistatinprotein SEQ ID NO:1. In some embodiments, the recombinant follistatinprotein includes an amino acid sequence at least 95% identical to thewild-type human Follistatin protein SEQ ID NO:1. In some embodiments,the recombinant follistatin protein includes an amino acid sequenceidentical to the wild-type human Follistatin protein SEQ ID NO:1.

In some embodiments, the recombinant follistatin protein comprises oneor more deletions, mutations or insertions as compared to the wild-typehuman Follistatin protein. In some embodiments, the recombinantfollistatin protein comprises a deletion of amino acids residues 212-288of SEQ ID NO:1 (which corresponds to domain 3). In some embodiments, therecombinant follistatin protein comprises the heparin binding site.

In some embodiments, the present invention provides methods of treatingDuchenne Muscular Dystrophy (DMD) including administering to anindividual who is suffering from or susceptible to DMD an effectiveamount of a recombinant follistatin protein such that at least onesymptom or feature of DMD is reduced in intensity, severity, orfrequency, or has delayed onset, wherein the recombinant follistatinprotein comprises an amino acid sequence at least 50% (e.g., at least55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or100%) identical to

(SEQ ID NO: 2) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCISISEDTEEEEEDEDQDYSFPISSILEW.

In some embodiments, the recombinant follistatin protein includes anamino acid sequence at least 70% identical to SEQ ID NO:2. In someembodiments, the recombinant follistatin protein includes an amino acidsequence at least 80% identical to SEQ ID NO:2. In some embodiments, therecombinant follistatin protein includes an amino acid sequence at least90% identical to SEQ ID NO:2. In some embodiments, the recombinantfollistatin protein includes an amino acid sequence at least 95%identical to SEQ ID NO:2. In some embodiments, the recombinantfollistatin protein includes an amino acid sequence identical to SEQ IDNO:2.

In some embodiments, the at least one symptom or feature of DMD isselected from the group consisting of muscle wasting, muscle weakness,muscle fragility, muscle hypertrophy, muscle pseudohypertrophy, jointcontracture, skeletal deformation, cardiomyopathy, impaired swallowing,impaired bowel and bladder function, muscle ischemia, cognitiveimpairment, behavioral dysfunction, socialization impairment, scoliosis,and impaired respiratory function.

In some embodiments, the recombinant follistatin protein is fused to anFc domain. In some embodiments, an Fc domain suitable for the presentinvention comprises an amino acid sequence at least 50% (e.g., at least55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or100%) identical to

(SEQ ID NO: 3) EPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK; or (SEQ ID NO: 4)KTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK; or (SEQ ID NO: 14)DKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK.

In some embodiments, the Fc domain comprises an amino acid sequence atleast 80% identical to SEQ ID NO: 3, 4, or 14. In some embodiments, theFc domain comprises an amino acid sequence at least 90% identical to SEQID NO: 3, 4, or 14. In some embodiments, the Fc domain comprises anamino acid sequence at least 95% identical to SEQ ID NO:3, 4, or 14.

In some embodiments, a suitable Fc domain comprises one or moremutations that improve binding between the Fc domain and the FcRnreceptor resulting in prolonged serum half-life. In some embodiments, asuitable Fc domain comprises one or more mutations at one or morepositions corresponding to Thr 250, Met 252, Ser 254, Thr 256, Thr 307,Glu 380, Met 428, His 433 and/or Asn 434 of human IgG1. In particularembodiments, a suitable Fc domain contains mutations H433K (His433Lys)and/or N434F (Asn434Phe). In particular embodiments, a suitable Fcdomain comprises a sequence shown below which incorporates the mutationsof H433K (His433Lys) and N434F (Asn434Phe):

(SEQ ID NO: 15) DKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQG NVFSCSVMHEAL KFHYTQKSLSLSPGK.

In some embodiments, a recombinant follistatin protein is fused to theFc domain via a linker. In some embodiments, the linker is a peptidecomprising 3-100 amino acids. In some embodiments, the linker is not alinker consisting of ALEVLFQGP (SEQ ID NO: 18). In some embodiments, thelinker comprises between 10-100, 10-90, 10-80, 10-70, 10-60, 10-50,10-40, 10-30, 10-20, 10-15 amino acids. In some embodiments, the linkercomprises at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, or 95 amino acids. In some embodiments, the linkercomprises a sequence at least 50% (e.g., at least 55%, 60%, 65%, 70%,75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99%) identical toGAPGGGGGAAAAAGGGGGGAP (GAG linker, SEQ ID NO: 5). In some embodiments,the linker comprises a sequence at least 50% (e.g., at least 55%, 60%,65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99%) identical toGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAP (GAG2 linker, SEQ ID NO: 6). Insome embodiments, the linker comprises a sequence at least 50% (e.g., atleast 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or99%) identical to GAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAP (GAG3 linker, SEQ ID NO:7). In some embodiments, the linkercomprises a sequence identical to SEQ ID NO:5, SEQ ID NO:6, or SEQ IDNO:7.

In some embodiments, the present invention provides a recombinantfollistatin fusion protein including a follistatin polypeptide, an Fcdomain, and a linker with a length of at least 10 (e.g., at least 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95) aminoacids that associates the follistatin polypeptide with the Fc domain. Insome embodiments, the present invention provides a recombinantfollistatin fusion protein including a follistatin polypeptide, an Fcdomain, and a linker that associates the follistatin polypeptide withthe Fc domain, wherein the linker is not a linker consisting ofALEVLFQGP (SEQ ID NO: 18). In some embodiments, a suitable follistatinpolypeptide comprises an amino acid sequence at least 50% (e.g., atleast 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%,or 100%) identical to the wild-type human Follistatin protein (SEQ IDNO: 1). In some embodiments, the recombinant follistatin fusion proteinis capable of binding to activin, myostatin and/or GDF-11 and has an invivo half-life ranging from about 0.5-10 days.

In particular embodiments, a recombinant follistatin protein suitablefor the present invention comprises an amino acid sequence at least 50%(e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%,98%, 99%, or 100%) identical to

SEQ ID NO: 8 GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 8), or SEQID NO: 9 GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSL SPGK (SEQ ID NO: 9).

In particular embodiments, a recombinant follistatin protein suitablefor the present invention comprises an amino acid sequence at least 50%(e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%,98%, 99%, or 100%) identical to SEQ ID NO:10

SEQ ID NO: 10 GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCISISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCS VMHEALHNHYTQKSLSLSPGK(SEQ ID NO: 10), or SEQ ID NO: 11GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCISISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 11).

In particular embodiments, a recombinant follistatin protein suitablefor the present invention comprises an amino acid sequence at least 50%(e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%,98%, 99%, or 100%) identical to

(SEQ ID NO: 16) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK Or (SEQ ID NO: 17)GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALKFHYTQKSLSLSPGK

In some embodiments, a recombinant follistatin protein suitable for thepresent invention is produced from mammalian cells. In some embodiments,the mammalian cells are human cells. In some embodiments, the mammaliancells are Chinese Hamster Ovary (CHO) cells or HT1080 cells.

It will be appreciated that embodiments of the invention may bedelivered via a variety of routes. In some embodiments, the recombinantfollistatin protein is administered systemically. In some embodiments,the systemic administration is selected from intravenous, intradermal,inhalation, transdermal (topical), intraocular, intramuscular,subcutaneous, intramuscular, oral, and/or transmucosal administration.

Embodiments may be administered via a multiplicity of dosing regimens.In some embodiments, the recombinant follistatin protein is administeredbimonthly, monthly, triweekly, biweekly, weekly, daily, or at variableintervals.

In some embodiments, the recombinant follistatin protein is delivered toone or more target tissues selected from striated muscle (e.g., skeletalmuscle, cardiac muscle). In some embodiments, the recombinantfollistatin protein is delivered to the heart. In some embodiments, therecombinant follistatin protein is delivered to skeletal muscle. In someembodiments, the recombinant follistatin protein is delivered to one ormore skeletal muscles selected from Table 1. In some embodiments, thestriated muscle (e.g., skeletal muscle) is selected from the groupconsisting of triceps, tibialis anterior, soleus, gastrocnemius, biceps,trapezius, deltoids, quadriceps, and diaphragm.

In some embodiments, the administration of the recombinant follistatinprotein results in muscle regeneration, fibrosis reduction, increasedmuscle strength, increased flexibility, increased range of motion,increased stamina, reduced fatigability, increased blood flow, improvedcognition, improved pulmonary function, inflammation inhibition, reducedmuscle fibrosis and/or necrosis.

In another aspect, the present invention provides compositions used invarious methods described herein. In some embodiments, the presentinvention provides recombinant follistatin fusion proteins including afollistatin polypeptide, an Fc domain, and a linker that associates thefollistatin polypeptide with the Fc domain, wherein the follistatinpolypeptide comprises an amino acid sequence at least at least 50%(e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%,98%, 99%, or 100%) identical to the wild-type human follistatin protein(SEQ ID NO:1). In some embodiments, the recombinant follistatin fusionprotein is capable of binding to activins, myostatin and/or GDF-11. Insome embodiments, the recombinant follistatin fusion protein has an invivo half-life greater than about 2 days (e.g., greater than about 2.5days, about 3 days, about 3.5 days, about 4 days, about 4.5 days, about5 days, about 5.5 days, about 6 days). In some embodiments, therecombinant follistatin fusion protein has an in vivo half-life rangingfrom about 2-10 days (e.g., ranging from about 2.5-10 days, from about3-10 days, from about 3.5-10 days, from about 4-10 days, from about4.5-10 days, from about 5-10 days, from about 3-8 days, from about 3.5-8days, from about 4-8 days, from about 4.5-8 days, from about 5-8 days,from about 3-6 days, from about 3.5-6 days, from about 4-6 days, fromabout 4.5-6 days, from about 5-6 days). In some embodiments, the in vivohalf-life is measured in one or more of mice, rats, non-human primates,and/or humans. In some embodiments, the follistatin polypeptide has anamino acid sequence at least 70% identical to the wild-type humanfollistatin protein (SEQ ID NO:1). In some embodiments, the follistatinpolypeptide has an amino acid sequence at least 80% identical to thewild-type human follistatin protein (SEQ ID NO:1). In some embodiments,the follistatin polypeptide has an amino acid sequence at least 90%identical to the wild-type human follistatin protein (SEQ ID NO:1). Insome embodiments, the follistatin polypeptide has an amino acid sequenceat least 95% identical to the wild-type human follistatin protein (SEQID NO:1). In some embodiments, the follistatin polypeptide has an aminoacid sequence identical to the wild-type human follistatin protein (SEQID NO:1). In some embodiments, the follistatin polypeptide contains adeletion of amino acids residues 212-288 of SEQ ID NO:1 (whichcorresponds to domain 3). In various embodiments, the follistatinpolypeptide contains the heparin sulfate binding site.

In some embodiments, the present invention provides recombinantfollistatin fusion proteins including a follistatin polypeptide, an Fcdomain, and a linker that associates the follistatin polypeptide withthe Fc domain, wherein the follistatin polypeptide comprises an aminoacid sequence at least 50% (e.g., at least 55%, 60%, 65%, 70%, 75%, 80%,85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100%) identical to

(SEQ ID NO: 2) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCISISEDTEEEEEDEDQDYSFPISSILEW.

In some embodiments, the recombinant follistatin fusion protein iscapable of binding to activins, myostatin and/or GDF-11. In someembodiments, the recombinant follistatin fusion protein has an in vivohalf-life greater than about 2 days (e.g., greater than about 2.5 days,about 3 days, about 3.5 days, about 4 days, about 4.5 days, about 5days, about 5.5 days, about 6 days). In some embodiments, therecombinant follistatin fusion protein has an in vivo half-life rangingfrom about 2-10 days (e.g., ranging from about 2.5-10 days, from about3-10 days, from about 3.5-10 days, from about 4-10 days, from about4.5-10 days, from about 5-10 days, from about 3-8 days, from about 3.5-8days, from about 4-8 days, from about 4.5-8 days, from about 5-8 days,from about 3-6 days, from about 3.5-6 days, from about 4-6 days, fromabout 4.5-6 days, from about 5-6 days). In some embodiments, the in vivohalf-life is measured in one or more of mice, rats, non-human primates,and/or humans.

In some embodiments, the Fc domain is an IgG1 Fc domain. In someembodiments, the Fc domain has an amino acid sequence at least 50%(e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%,98%, 99%, or 100%) identical to

(SEQ ID NO: 3) EPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK; or (SEQ ID NO: 4)KTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK; or (SEQ ID NO: 14)DKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK.

In some embodiments, a suitable Fc domain comprises one or moremutations that improve binding between the Fc domain and the FcRnreceptor resulting in prolonged serum half-life. In some embodiments,the Fc domain comprises one or more mutations at one or more positionscorresponding to Thr 250, Met 252, Ser 254, Thr 256, Thr 307, Glu 380,Met 428, His 433, and/or Asn 434 of human IgG1. In particularembodiments, a suitable Fc domain contains mutations H433K (His433Lys)and/or N434F (Asn434Phe). In particular embodiments, a suitable Fcdomain comprises a sequence shown below which incorporates the mutationsof H433K (His433Lys) and N434F (Asn434Phe):

(SEQ ID NO: 15) DKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQG NVFSCSVMHEAL KFHYTQKSLSLSPGK.

In some embodiments, a recombinant follistatin fusion protein accordingto the present invention includes a linker such that the Fc fusion viathe linker does not substantially change the binding properties offollistatin to cognate ligands, including maintaining the lack ofbinding to heparin. In some embodiments, a suitable linker is a peptidecomprising 3-60 amino acids. In some embodiments, a suitable linker is apeptide comprising at least 10 (e.g., at least 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95) amino acids. In someembodiments, a suitable linker comprises a sequence at least 50% (e.g.,at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%,99%, or 100%) identical to GAPGGGGGAAAAAGGGGGGAP (GAG linker, SEQ ID NO:5). In some embodiments, a suitable linker comprises a sequence at least50% (e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%,97%, 98%, 99%, or 100%) identical toGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAP (GAG2 linker, SEQ ID NO: 6). Insome embodiments, a suitable linker comprises a sequence at least 50%(e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%,98%, 99%, or 100%) identical toGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGG GAP (GAG3 linker,SEQ ID NO:7).

In particular embodiments, a recombinant follistatin fusion proteinprovided by the present invention comprises an amino acid sequence atleast 50% (e.g., at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%,96%, 97%, 98%, 99%, or 100%) identical to SEQ ID NO:8, 9, 10, 11, 16 or17:

In some embodiments, the present invention provides nucleic acidscomprising a nucleotide sequence encoding a recombinant follistatinfusion protein described herein. In some embodiments, the presentinvention provides a cell comprising a nucleic acid comprising anucleotide sequence encoding a recombinant follistatin fusion proteindescribed herein. In some embodiments, the present invention providespharmaceutical compositions comprising a recombinant follistatin fusionprotein described herein and a pharmaceutically acceptable carrier.

As used in this application, the terms “about” and “approximately” areused as equivalents. Any numerals used in this application with orwithout about/approximately are meant to cover any normal fluctuationsappreciated by one of ordinary skill in the relevant art.

Other features, objects, and advantages of the present invention areapparent in the detailed description that follows. It should beunderstood, however, that the detailed description, while indicatingembodiments of the present invention, is given by way of illustrationonly, not limitation. Various changes and modifications within the scopeof the invention will become apparent to those skilled in the art fromthe detailed description.

BRIEF DESCRIPTION OF THE DRAWING

The drawings are for illustration purposes only not for limitation.

FIG. 1 shows exemplary results illustrating that FS315-Fc does notinhibit BMP-9 or BMP-10 signaling through the Smad 1/5/8 pathway ascompared to a commercially available soluble activin receptor (sActRIIB)FIG. 1A shows exemplary results of the BMP-9 inhibition assay and FIG.1B shows exemplary results of the BMP-10 inhibition assay. FS315-Fc doesnot inhibit BMP-9 or -10 signaling through Smad 1/5/8 pathway(BRE-luciferase reporter assay).

FIG. 2 shows exemplary results illustrating that FS315-Fc inhibitsmyostatin- and activin-mediated Smad 2/3 signaling. FIG. 2A showsexemplary results of the myostatin inhibition assay and FIG. 2B showsexemplary results of an activin A inhibition assay. FS315-GAG3-mFcinhibits myostatin and activin A signaling through Smad2/3 pathway(CAGA-luciferase reporter assay).

FIG. 3 shows exemplary results illustrating PK profile across tissues.An exemplary follistatin-Fc protein has a serum half-life of ˜5 days inmouse serum (FIG. 3A) and a tissue half-life of 2-5 days (FIG. 3B). FIG.3 shows FS315-mFc PK profile in mouse serum and tissue after SCinjection of 1 mg/kg. Estimated tissue half-life is 2-5 days, serumhalf-life is ˜5 days.

FIG. 4 shows exemplary results illustrating the effect of an exemplaryfollistatin-Fc protein on muscle weight of quadriceps (FIG. 4A),gastrocnemius (FIG. 4B), tibialis anterior (FIG. 4C), and triceps (FIG.4D) after 4 and 10 weeks of exposure to 1 mg/kg FS315-mFc and 6 weeksexposure to 8 mg/kg. The muscle weights are corrected to baseline bodyweight. FIG. 4 shows changes in muscle mass after twice weekly SCadministration of FS315-mFc into mdx mice. The muscle weights arenormalized to baseline body weight. There is a trend for increasedmuscle weight in mdx mice treated with 1 mg/kg for 10 weeks or 8 mg/kgfor 6 weeks.

FIG. 5 shows exemplary results illustrating the effect of exemplaryfollistatin-Fc protein on serum follistatin levels over time. FIG. 5A.shows the levels in the serum after treatment with 1 mg/kg FS315-mFcover 10 weeks, and FIG. 5B. shows the levels in the serum aftertreatment with 8 mg/kg FS315-mFc over 6 weeks. FIG. 5 shows the levelsof FS315-mFc in serum of mdx mice treated with 1 mg/kg (FIG. 5A) and 8mg/kg (FIG. 5B).

FIG. 6 shows exemplary results illustrating the effect of exemplaryfollistatin-Fc protein on muscle weight of the gastrocnemius afterexposure to FS315-mFc, sActRIIB-mFc, or PBS control. FIG. 6 shows theeffect of intramuscular injection of FS315-mFc on muscle weight after 4weeks of twice weekly injection of 20 μg directly into the gastrocnemiusmuscle. The contra-lateral gastrocnemius muscle received an equivalentvolume of PBS and acts as the control for each treatment group. Theuntreated group did not receive injections, and each data set for thisgroup represents right and left gastrocnemius muscles. P-values obtainedfrom paired t-test with Bonferroni correction.

FIG. 7 shows exemplary results illustrating the effects of follistatinwild-type and variants on body weight. Panel A shows exemplary averagebody weight of animals in each group over time, and panel B showsexemplary average body weight of animals in each group at week 6post-injection. FIG. 7 shows weekly body weight after intramuscular genedelivery of follistatin variants to gastrocnemius and quadriceps muscleof C57 mice.

FIG. 8 shows exemplary results illustrating the effect of follistatinvariants on the weight of injected muscle at week 2 post-injection.Panel A shows the mass of the injected muscle gastrocnemius while panelB shows the mass of the injected muscle quadriceps. FIG. 8 shows week 2muscle weights after intramuscular gene delivery of follistatin variantsto gastrocnemius (FIG. 8, panel A) and quadriceps (FIG. 8, panel B)muscle of C57 mice.

FIG. 9 shows exemplary results illustrating the effect of domain 3deletion on injected muscle and muscle remote from the injection sitetwo weeks post-injection. The left quadriceps was a site of injectionwhile the right quadriceps is the contralateral intra-animal controlmuscle. FIG. 9 shows week 2 gross morphology of dissected quadricepsmuscle receiving dFSD3 via direct gene delivery. The right quad muscledid not receive an injection of dFSD3.

FIG. 10 shows exemplary results illustrating the effect of follistatinvariants on the weight of specific muscles in injection site and distalfrom the injection site at week 4 post-injection. Panel A(gastrocnemius) and panel B (quadriceps) are injected muscle. Panel C(tibialis anterior), Panel D (triceps) and Panel E (diaphragm) aremuscle distal from injection site. FIG. 10 shows week 4 muscle weightsafter intramuscular gene delivery of follistatin variants togastrocnemius (FIG. 10, panel A), and quadriceps muscle (FIG. 10, panelB) of C57 mice. The following muscles were remote from the injectionsite: tibialis anterior (FIG. 10, panel C), triceps (FIG. 10, panel D),and diaphragm (FIG. 10, panel E).

FIG. 11 shows exemplary results illustrating the effect of domain 3deletion on injected muscle and muscle remote from the injection sitefour weeks post-injection. The left quadriceps was a site of injectionwhile the right quadriceps is the contralateral intra-animal controlmuscle. FIG. 11 shows week 4 gross morphology of quadriceps musclereceiving dFSD3 via direct gene delivery. The right quad muscle did notreceive an injection of dFSD3.

FIG. 12 shows exemplary results illustrating the effect of follistatinvariants on fiber size in both injected muscles and distal muscles atweek 2 post-injection in the (A) quadriceps, (B) gastrocnemius, (C)tibialis anterior, (D) triceps, and (E) diaphragm. FIG. 12 shows week 2muscle myofiber diameter after intramuscular gene delivery offollistatin variants to quadriceps (FIG. 12, panel A) and gastrocnemiusmuscle (FIG. 12, panel B) of C57 mice. The following muscles were remotefrom the injection site: tibialis anterior (FIG. 12, panel C), triceps(FIG. 12, panel D), and diaphragm (FIG. 12, panel E).

FIG. 13 shows exemplary results illustrating the effect of follistatinvariants on fiber size in both injected muscles and distal muscles atweek 4 post-injection, in the (A) quadriceps, (B) gastrocnemius, (C)tibialis anterior, (D) triceps, and (E) diaphragm. FIG. 13 shows week 4muscle myofiber diameter after intramuscular gene delivery offollistatin variants to quadriceps (FIG. 13, panel A) and gastrocnemiusmuscle (FIG. 13, panel B) of C57 mice. The following muscles were remotefrom the injection site: tibialis anterior (FIG. 13, panel C), triceps(FIG. 13, panel D), and diaphragm (FIG. 13, panel E).

FIG. 14 shows exemplary results illustrating the effect of follistatinvariants on fiber size in both injected muscles and distal muscles atweek 6 post-injection, in the (A) quadriceps, (B) gastrocnemius, (C)tibialis anterior, (D) triceps, and (E) diaphragm. FIG. 14 shows week 6muscle myofiber diameter after intramuscular gene delivery offollistatin variants to quadriceps (FIG. 14, panel A) and gastrocnemiusmuscle (FIG. 14, panel B) of C57 mice. The following muscles were remotefrom the injection site: tibialis anterior (FIG. 14, panel C), triceps(FIG. 14, panel D), and diaphragm (FIG. 14, panel E).

FIG. 15 shows exemplary results demonstrating the effect of an exemplaryfollistatin-Fc protein on the diameter of myofibers in the gastrocnemiusof A) C57 mice and B) mdx mice after 4 weeks of exposure. FIG. 15 showssize distribution of myofibers after intramuscular FS315-mFc injectioninto the gastrocnemius of C57 (WT) (FIG. 15, panel A) or mdx (FIG. 15,panel B) mice.

FIG. 16 shows exemplary results demonstrating the effect of an exemplaryfollistatin-Fc protein on the body weight of treated C57 mice after 2,4, 6, or 8 weeks of exposure, as compared to vehicle control animals.FIG. 16 shows body weights of C57 mice treated twice weekly for 8 weekswith 10 mg/kg FS315-mFc via subcutaneous injection. P values wereobtained using unpaired t-test.

FIG. 17 shows exemplary results demonstrating the effect of an exemplaryfollistatin-Fc protein on the weight of the triceps and quadriceps oftreated animals as a percent increase over vehicle control animals,after 4 and 8 weeks of exposure. FIG. 17 shows percent change in weightfor triceps and quadriceps muscles in FS315-mFc treated C57 mice at week4 and 8 is shown. P values were obtained from unpaired t-test.

FIG. 18 shows exemplary results demonstrating the effect of an exemplaryfollistatin-Fc protein on the diameter of myofibers in the triceps andquadriceps of treated animals as percent increase over vehicle controlanimals after 4 and 8 weeks of exposure. FIG. 18 shows percent increaseover vehicle control of triceps and quadriceps myofiber diameters inFS315-mFc treated C57 mice at week 4 and 8. P values were obtained fromunpaired t-test.

FIG. 19 shows exemplary levels of follistatin-Fc protein in the serum ofanimals administered the fusion protein via twice weekly subcutaneousinjection after 1, 3, 4, 6, or 8 weeks of exposure. Panel A) shows theresults from animals euthanized after 4 weeks and panel B) shows theresults from animals euthanized after 8 weeks of exposure. FIG. 19 showslevels of FS315-mFc in serum after twice weekly subcutaneous injectionof 10 mg/kg into C57 mice. On the X-axis, “Week” refers to week oftreatment course. The number of days post-injection of FS315-mFc,corresponding to when the serum was collected, is included inparentheses. The vehicle treated mice had no detectable follistatin inthe serum.

FIG. 20 shows exemplary results demonstrating the effect offollistatin-Fcprotein on the mRNA expression of three markers offibrosis: alpha-smooth muscle actin, collagen triple helix repeatcontaining 1 protein (cthrc1), and collagen I, in the quadriceps oftreated animals as compared to vehicle control animals after 6 or 12weeks of exposure. FIG. 20 shows mRNA levels of key markers of fibrosisafter 6 and 12 weeks of FS315-mFc treatment of mdx mice. RT-PCR was usedto quantitate mRNA levels of each protein in quadriceps of treated mice(n=15 animals per time point). P-values were obtained from a one-wayANOVA followed by Tukey's posthoc pairwise comparison test or itsnonparametric analogue.

FIG. 21 shows exemplary H&E stained sections of quadriceps and tricepstissue of mdx mice treated with vehicle or follistatin-Fc protein forsix weeks. Also shown are exemplary H&E stains from the quadriceps andtriceps of C57 control mice. FIG. 21 shows H&E stained sections ofquadriceps and triceps muscle after 6 weeks of twice weekly treatmentwith 10 mg/kg FS315-mFc. The outlined areas indicate necrotic tissue.The C57 panel represents healthy, unaffected muscle.

FIG. 22 shows exemplary collagen I stained sections of quadriceps,triceps, and diaphragm tissue of mdx mice treated with vehicle orfollistatin-Fc protein for twelve weeks. Also shown are exemplarycollagen I stains from the quadriceps, triceps and diaphragm of C57control mice. FIG. 22 shows collagen I stained sections of diaphragm,quadriceps and triceps muscle after 12 weeks of twice weekly treatmentwith 10 mg/kg FS315-mFc. The stained areas indicate collagen Ideposition and fibrosis. The C57 panel represents healthy, unaffectedmuscle.

FIG. 23 shows exemplary results demonstrating the effects of twiceweekly intramuscular injections of one of two follistatin variants, aFS315-mFc fusion protein and a dFSD3-mFc variant fusion protein, on themuscle weights of C57BL/10 mice treated for four weeks as compared tothe contra-lateral vehicle control muscle. FIG. 23 shows thepharmacodynamics effect of FS315-mFc and dFSD3-mFc on injected muscleweights after twice weekly injections of 20 μg directly into thegastrocnemius muscle for 4 weeks. P values were obtained from pairedt-test (follistatin treated compared to vehicle control).

FIG. 24 shows exemplary results demonstrating that the FS315-GAG3-mFcand FS315-GAG3-hFc fusion proteins inhibit (A) myostatin and (B) activinsignaling in the CAGA-luciferase assay to the same extent as nativeFS315. In comparison, Sino Biological FS315-hFc (manufactured by SinoBiological Inc. Catalog Number 10685-H02H) which contains a 9 amino acidlinker is significantly less potent. FIG. 24 shows FS315-GAG-mFc and-hFc inhibit (A) myostatin and (B) activin signaling through Smad2/3pathway (CAGA-luciferase reporter assay) to a greater extent compared tothe commercially available FS315-(9 linker)-hFc protein (Sinobiological).

FIG. 25 shows levels of FS315-GAG3-hFc protein in the serum of ratsdosed with a single SC injection of 10 mg/kg protein. The calculatedserum half-life was 3.5 days. FIG. 25 shows FS315-hFc PK profile in ratserum after SC injection of 10 mg/kg. Estimated serum half-life ˜3.5days.

DEFINITIONS

In order for the present invention to be more readily understood,certain terms are first defined below. Additional definitions for thefollowing terms and other terms are set forth throughout thespecification.

Animal: As used herein, the term “animal” refers to any member of theanimal kingdom. In some embodiments, “animal” refers to humans, at anystage of development. In some embodiments, “animal” refers to non-humananimals, at any stage of development. In certain embodiments, thenon-human animal is a mammal (e.g., a rodent, a mouse, a rat, a rabbit,a monkey, a dog, a cat, a sheep, cattle, a primate, and/or a pig). Insome embodiments, animals include, but are not limited to, mammals,birds, reptiles, amphibians, fish, insects, and/or worms. In someembodiments, an animal may be a transgenic animal,genetically-engineered animal, and/or a clone.

Approximately or about: As used herein, the term “approximately” or“about,” as applied to one or more values of interest, refers to a valuethat is similar to a stated reference value. In certain embodiments, theterm “approximately” or “about” refers to a range of values that fallwithin 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%,8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greaterthan or less than) of the stated reference value unless otherwise statedor otherwise evident from the context (except where such number wouldexceed 100% of a possible value).

Bioavailability: As used herein, the term “bioavailability” generallyrefers to the percentage of the administered dose that reaches the bloodstream of a subject.

Biologically active: As used herein, the phrase “biologically active”refers to a characteristic of any agent that has activity in abiological system, and particularly in an organism. For instance, anagent that, when administered to an organism, has a biological effect onthat organism, is considered to be biologically active. In particularembodiments, where a peptide is biologically active, a portion of thatpeptide that shares at least one biological activity of the peptide istypically referred to as a “biologically active” portion.

Cardiac Muscle: As used herein, the term “cardiac muscle” refers to atype of involuntary striated muscle found in the walls of the heart, andparticularly the myocardium.

Carrier or diluent: As used herein, the terms “carrier” and “diluent”refers to a pharmaceutically acceptable (e.g., safe and non-toxic foradministration to a human) carrier or diluting substance useful for thepreparation of a pharmaceutical formulation. Exemplary diluents includesterile water, bacteriostatic water for injection (BWFI), a pH bufferedsolution (e.g. phosphate-buffered saline), sterile saline solution,Ringer's solution or dextrose solution.

Follistatin or recombinant follistatin: As used herein, the term“follistatin (FS)” or “recombinant follistatin” refers to any wild-typeand modified follistatin proteins (e.g., follistatin proteins with aminoacid mutations, deletions, insertions, and/or fusion proteins) thatretain substantial follistatin biological activity unless otherwisespecified. A non-limiting example of deletions is a domain 3 deletion(ΔD3 or dFSD3). A non-limiting example of fusion proteins is anFc-fusion protein.

Functional equivalent or derivative: As used herein, the term“functional equivalent” or “functional derivative” denotes, in thecontext of a functional derivative of an amino acid sequence, a moleculethat retains a biological activity (either function or structural) thatis substantially similar to that of the original sequence. A functionalderivative or equivalent may be a natural derivative or is preparedsynthetically. Exemplary functional derivatives include amino acidsequences having substitutions, deletions, or additions of one or moreamino acids, provided that the biological activity of the protein isconserved. The substituting amino acid desirably has chemico-physicalproperties which are similar to that of the substituted amino acid.Desirable similar chemico-physical properties include, similarities incharge, bulkiness, hydrophobicity, hydrophilicity, and the like.

Fusion protein: As used herein, the term “fusion protein” or “chimericprotein” refers to a protein created through the joining of two or moreoriginally separate proteins, or portions thereof. In some embodiments,a linker or spacer will be present between each protein.

Half-Life: As used herein, the term “half-life” is the time required fora quantity such as protein concentration or activity to fall to half ofits value as measured at the beginning of a time period.

Hypertrophy: As used herein the term “hypertrophy” refers to theincrease in volume of an organ or tissue due to the enlargement of itscomponent cells.

Improve, increase, or reduce: As used herein, the terms “improve,”“increase” or “reduce,” or grammatical equivalents, indicate values thatare relative to a baseline measurement, such as a measurement in thesame individual prior to initiation of the treatment described herein,or a measurement in a control subject (or multiple control subject) inthe absence of the treatment described herein. A “control subject” is asubject afflicted with the same form of disease as the subject beingtreated, who is about the same age as the subject being treated.

In Vitro: As used herein, the term “in vitro” refers to events thatoccur in an artificial environment, e.g., in a test tube or reactionvessel, in cell culture, etc., rather than within a multi-cellularorganism.

In Vivo: As used herein, the term “in vivo” refers to events that occurwithin a multi-cellular organism, such as a human and a non-humananimal. In the context of cell-based systems, the term may be used torefer to events that occur within a living cell (as opposed to, forexample, in vitro systems).

Linker: As used herein, the term “linker” refers to, in a fusionprotein, an amino acid sequence other than that appearing at aparticular position in the natural protein and is generally designed tobe flexible or to interpose a structure, such as an a-helix, between twoprotein moieties. A linker is also referred to as a spacer. A linker ora spacer typically does not have biological function on its own.

Polypeptide: The term “polypeptide” as used herein refers to asequential chain of amino acids linked together via peptide bonds. Theterm is used to refer to an amino acid chain of any length, but one ofordinary skill in the art will understand that the term is not limitedto lengthy chains and can refer to a minimal chain comprising two aminoacids linked together via a peptide bond. As is known to those skilledin the art, polypeptides may be processed and/or modified. As usedherein, the terms “polypeptide” and “peptide” are used inter-changeably.

Prevent: As used herein, the term “prevent” or “prevention”, when usedin connection with the occurrence of a disease, disorder, and/orcondition, refers to reducing the risk of developing the disease,disorder and/or condition. See the definition of “risk.”

Protein: The term “protein” as used herein refers to one or morepolypeptides that function as a discrete unit. If a single polypeptideis the discrete functioning unit and does not require permanent ortemporary physical association with other polypeptides in order to formthe discrete functioning unit, the terms “polypeptide” and “protein” maybe used interchangeably. If the discrete functional unit is comprised ofmore than one polypeptide that physically associate with one another,the term “protein” refers to the multiple polypeptides that arephysically coupled and function together as the discrete unit.

Risk: As will be understood from context, a “risk” of a disease,disorder, and/or condition comprises a likelihood that a particularindividual will develop a disease, disorder, and/or condition (e.g.,muscular dystrophy). In some embodiments, risk is expressed as apercentage. In some embodiments, risk is from 0, 1, 2, 3, 4, 5, 6, 7, 8,9, 10, 20, 30, 40, 50, 60, 70, 80, 90 up to 100%. In some embodimentsrisk is expressed as a risk relative to a risk associated with areference sample or group of reference samples. In some embodiments, areference sample or group of reference samples have a known risk of adisease, disorder, condition and/or event (e.g., muscular dystrophy). Insome embodiments a reference sample or group of reference samples arefrom individuals comparable to a particular individual. In someembodiments, relative risk is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more.

Striated muscle: As used herein, the term “striated muscle” refers tomultinucleated muscle tissue with regular arrangement of theirintracellular contractile units, sarcomeres, leading to the appearanceof striations using microscopy and under voluntary control. Typically,striated muscle can be cardiac muscle, skeletal muscle, andBranchiomeric muscles.

Smooth muscle: As used herein, the term “smooth muscle” refers toinvoluntarily controlled, non-striated muscle, including unitary andmulti-unit muscle.

Subject: As used herein, the term “subject” refers to a human or anynon-human animal (e.g., mouse, rat, rabbit, dog, cat, cattle, swine,sheep, horse or primate). A human includes pre- and post-natal forms. Inmany embodiments, a subject is a human being. A subject can be apatient, which refers to a human presenting to a medical provider fordiagnosis or treatment of a disease. The term “subject” is used hereininterchangeably with “individual” or “patient.” A subject can beafflicted with or is susceptible to a disease or disorder but may or maynot display symptoms of the disease or disorder.

Substantially: As used herein, the term “substantially” refers to thequalitative condition of exhibiting total or near-total extent or degreeof a characteristic or property of interest. One of ordinary skill inthe biological arts will understand that biological and chemicalphenomena rarely, if ever, go to completion and/or proceed tocompleteness or achieve or avoid an absolute result. The term“substantially” is therefore used herein to capture the potential lackof completeness inherent in many biological and chemical phenomena.

Substantial homology: The phrase “substantial homology” is used hereinto refer to a comparison between amino acid or nucleic acid sequences.As will be appreciated by those of ordinary skill in the art, twosequences are generally considered to be “substantially homologous” ifthey contain homologous residues in corresponding positions. Homologousresidues may be identical residues. Alternatively, homologous residuesmay be non-identical residues will appropriately similar structuraland/or functional characteristics. For example, as is well known bythose of ordinary skill in the art, certain amino acids are typicallyclassified as “hydrophobic” or “hydrophilic” amino acids., and/or ashaving “polar” or “non-polar” side chains Substitution of one amino acidfor another of the same type may often be considered a “homologous”substitution.

As is well known in this art, amino acid or nucleic acid sequences maybe compared using any of a variety of algorithms, including thoseavailable in commercial computer programs such as BLASTN for nucleotidesequences and BLASTP, gapped BLAST, and PSI-BLAST for amino acidsequences. Exemplary such programs are described in Altschul, et al.,Basic local alignment search tool, J. Mol. Biol., 215(3): 403-410, 1990;Altschul, et al., Methods in Enzymology; Altschul, et al., “Gapped BLASTand PSI-BLAST: a new generation of protein database search programs”,Nucleic Acids Res. 25:3389-3402, 1997; Baxevanis, et al.,Bioinformatics: A Practical Guide to the Analysis of Genes and Proteins,Wiley, 1998; and Misener, et al., (eds.), Bioinformatics Methods andProtocols (Methods in Molecular Biology, Vol. 132), Humana Press, 1999.In addition to identifying homologous sequences, the programs mentionedabove typically provide an indication of the degree of homology. In someembodiments, two sequences are considered to be substantially homologousif at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, 99% or more of their corresponding residues arehomologous over a relevant stretch of residues. In some embodiments, therelevant stretch is a complete sequence. In some embodiments, therelevant stretch is at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60,65, 70, 75, 80, 85, 90, 95, 100, 125, 150, 175, 200, 225, 250, 275, 300,325, 350, 375, 400, 425, 450, 475, 500 or more residues.

Substantial identity: The phrase “substantial identity” is used hereinto refer to a comparison between amino acid or nucleic acid sequences.As will be appreciated by those of ordinary skill in the art, twosequences are generally considered to be “substantially identical” ifthey contain identical residues in corresponding positions. As is wellknown in this art, amino acid or nucleic acid sequences may be comparedusing any of a variety of algorithms, including those available incommercial computer programs such as BLASTN for nucleotide sequences andBLASTP, gapped BLAST, and PSI-BLAST for amino acid sequences. Exemplarysuch programs are described in Altschul, et al., Basic local alignmentsearch tool, J. Mol. Biol., 215(3): 403-410, 1990; Altschul, et al.,Methods in Enzymology; Altschul et al., Nucleic Acids Res. 25:3389-3402,1997; Baxevanis et al., Bioinformatics: A Practical Guide to theAnalysis of Genes and Proteins, Wiley, 1998; and Misener, et al.,(eds.), Bioinformatics Methods and Protocols (Methods in MolecularBiology, Vol. 132), Humana Press, 1999. In addition to identifyingidentical sequences, the programs mentioned above typically provide anindication of the degree of identity. In some embodiments, two sequencesare considered to be substantially identical if at least 50%, 55%, 60%,65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%,99% or more of their corresponding residues are identical over arelevant stretch of residues. In some embodiments, the relevant stretchis a complete sequence. In some embodiments, the relevant stretch is atleast 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400,425, 450, 475, 500 or more residues.

Suffering from: An individual who is “suffering from” a disease,disorder, and/or condition has been diagnosed with or displays one ormore symptoms of the disease, disorder, and/or condition.

Susceptible to: An individual who is “susceptible to” a disease,disorder, and/or condition has not been diagnosed with the disease,disorder, and/or condition. In some embodiments, an individual who issusceptible to a disease, disorder, and/or condition may not exhibitsymptoms of the disease, disorder, and/or condition. In someembodiments, an individual who is susceptible to a disease, disorder,condition, or event (for example, DMD) may be characterized by one ormore of the following: (1) a genetic mutation associated withdevelopment of the disease, disorder, and/or condition; (2) a geneticpolymorphism associated with development of the disease, disorder,and/or condition; (3) increased and/or decreased expression and/oractivity of a protein associated with the disease, disorder, and/orcondition; (4) habits and/or lifestyles associated with development ofthe disease, disorder, condition, and/or event (5) having undergone,planning to undergo, or requiring a transplant. In some embodiments, anindividual who is susceptible to a disease, disorder, and/or conditionwill develop the disease, disorder, and/or condition. In someembodiments, an individual who is susceptible to a disease, disorder,and/or condition will not develop the disease, disorder, and/orcondition.

Target tissues: As used herein, the term “target tissues” refers to anytissue that is affected by a disease to be treated such as Duchennemuscular dystrophy (DMD). In some embodiments, target tissues includethose tissues that display disease-associated pathology, symptom, orfeature, including but not limited to muscle wasting, skeletaldeformation, cardiomyopathy, and impaired respiratory function.

Therapeutically effective amount: As used herein, the term“therapeutically effective amount” of a therapeutic agent means anamount that is sufficient, when administered to a subject suffering fromor susceptible to a disease, disorder, and/or condition, to treat,diagnose, prevent, and/or delay the onset of the symptom(s) of thedisease, disorder, and/or condition. It will be appreciated by those ofordinary skill in the art that a therapeutically effective amount istypically administered via a dosing regimen comprising at least one unitdose.

Treating: As used herein, the term “treat,” “treatment,” or “treating”refers to any method used to partially or completely alleviate,ameliorate, relieve, inhibit, prevent, delay onset of, reduce severityof and/or reduce incidence of one or more symptoms or features of aparticular disease, disorder, and/or condition. Treatment may beadministered to a subject who does not exhibit signs of a disease and/orexhibits only early signs of the disease for the purpose of decreasingthe risk of developing pathology associated with the disease.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The present invention provides, among other things, methods andcompositions for treating muscular dystrophy, including Duchennemuscular dystrophy (DMD) and/or Becker Muscular Dystrophy, based onfollistatin as a protein therapeutic. In some embodiments, the presentinvention provides methods of treating DMD including administering to anindividual who is suffering from or susceptible to DMD an effectiveamount of a recombinant follistatin protein such that at least onesymptom or feature of DMD is reduced in intensity, severity, orfrequency, or has delayed onset.

Various aspects of the invention are described in detail in thefollowing sections. The use of sections is not meant to limit theinvention. Each section can apply to any aspect of the invention. Inthis application, the use of “or” means “and/or” unless statedotherwise.

Duchenne Muscular Dystrophy (DMD)

DMD is a disease characterized by progressive deterioration of musclesand loss of muscle related functions throughout the body. It iscontemplated that the present invention provides methods andcompositions for regenerating muscle and treating fibrosis, inflammationand other symptoms or features associated with DMD and other musculardystrophies in various muscle tissues. In some embodiments, use ofprovided methods and compositions in a subject result in a decreasefibrosis and/or necrosis in that subject.

Muscle Tissues

There are two major types of muscle tissue in an animal—striated muscleand smooth muscle. As used herein, the term “striated muscle” refers tomuscle tissues containing repeating sarcomeres. Striated muscle tends tobe under voluntary control and attached to the skeleton, though thereare some exceptions, such as cardiac muscle, which has severalproperties of striated muscle, but is not under voluntary control.Generally, striated muscle allows for voluntary movement of the body andincludes the major muscle groups including the quadriceps,gastrocnemius, biceps, triceps, trapezius, deltoids, and many others.Striated muscle tends to be very long and, many striated muscles areable to function independently. Some striated muscle, however, is notattached to the skeleton, including those in the mouth, anus, heart, andupper portion of the esophagus.

Smooth muscle, on the other hand, has very different structure. Ratherthan a series of long muscles with separate skeletal attachments, smoothmuscle tends to be organized into continuous sheets with mechanicallinkages between smooth muscle cells. Smooth muscle is often located inthe walls of hollow organs and is usually not under voluntary control.Smooth muscles lining a particular organ must bear the same load andcontract concurrently. Smooth muscle functions, at least in part, tohandle changes in load on hollow organs caused by movement and/orchanges in posture or pressure. This dual role means that smooth musclemust not only be able to contract like striated muscle, but also that itmust be able to contract tonically to maintain organ dimensions againstsustained loads. Examples of smooth muscles are those lining bloodvessels, bladder, gastrointestinal track such as rectum.

The strength of a muscle depends on the number and sizes of the muscle'scells and on their anatomic arrangement. Increasing the diameter of amuscle fiber either by the increase in size of existing myofibrils(hypertrophy) and/or the formation of more muscle cells (hyperplasia)will increase the force-generating capacity of the muscle.

Muscles may also be grouped by location or function. In someembodiments, a recombinant follistatin protein is targeted to one ormore muscles of the face, one or more muscles for mastication, one ormore muscles of the tongue and neck, one or more muscles of the thorax,one or more muscles of the pectoral girdle and arms, one or more musclesof the arm and shoulder, one or more ventral and dorsal forearm muscles,one or more muscles of the hand, one or more muscles of the erectorspinae, one or more muscles of the pelvic girdle and legs, and/or one ormore muscles of the foreleg and foot.

In some embodiments, muscles of the face include, but are not limitedto, intraocular muscles such as ciliary, iris dilator, iris sphincter;muscles of the ear such as auriculares, temporoparietalis, stapedius,tensor tympani; muscles of the nose such as procerus, nasalis, dilatornaris, depressor septi nasi, levator labii superioris alaeque nasi;muscles of the mouth such as levator anguli oris, depressor anguli oris,orbicularis oris, Buccinator, Zygomaticus Major and Minor, Platysma,Levator Labii Superioris, Depressor Labii Inferioris, Risorius,Mentalis, and/or Corrugator Supercilii.

In some embodiments, muscles of mastication include, but are not limitedto, Masseter, Temporalis, Medial Pterygoid, Lateral Pterygoid. In someembodiments, muscles of the tongue and neck include, but are not limitedto, Genioglossus, Styloglossus, Palatoglossus, Hyoglossus, Digastric,Stylohyoid, Mylohyoid, Geniohyoid, Omohyoid, Sternohyoid, Sternothyroid,Thyrohyoid, Sternocleidomastoid, Anterior Scalene, Middle Scalene,and/or Posterior Scalene.

In some embodiments, muscles of the thorax, pectoral girdle, and armsinclude, but are not limited to, Subclavius Pectoralis major, Pectoralisminor, Rectus abdominis, External abdominal oblique, Internal abdominaloblique, Transversus Abdominis, Diaphragm, External Intercostals,Internal Intercostals, Serratus Anterior, Trapezius, Levator Scapulae,Rhomboideus Major, Rhomboideus Minor, Latissimus dorsi, Deltoid,subscapularis, supraspinatus, infraspinatus, Teres major, Teres minor,and/or Coracobrachialis.

In some embodiments, muscles of the arm and shoulder include, but arenot limited to, Biceps brachii-Long Head, Biceps brachii-Short Head,Triceps brachii-Long Head, Triceps brachii Lateral Head, Tricepsbrachii-Medial Head, Anconeus, Pronator teres, Supinator, and/orBrachialis.

In some embodiments, muscles of the ventral and dorsal forearm include,but are not limited to, Brachioradialis, Flexor carpi radialis, Flexorcarpi ulnaris, Palmaris longus, Extensor carpi ulnaris, Extensor carpiradialis longus, Extensor carpi radialis brevis, Extensor digitorum,Extensor digiti minimi.

In some embodiments, muscles of the hand include, but are not limited tointrinsic muscles of the hand such as thenar, abductor pollicis brevis,flexor pollicis brevis, opponens pollicis, hypothenar, abductor digitiminimi, the flexor digiti minimi brevis, opponens digiti minimi, palmarinterossei, dorsal interossei and/or lumbricals.

In some embodiments, muscles of the erector spinae include, but are notlimited to, cervicalis, spinalis, longissimus, and/or iliocostalis.

In some embodiments, muscles of the pelvic girdle and the legs include,but are not limited to, Psoas Major, Iliacus, quadratus femoris,Adductor longus, Adductor brevis, Adductor magnus, Gracilis, Sartorius,Quadriceps femoris such as, rectus femoris, vastus lateralis, vastusmedialis, vastus intermedius, Gastrocnemius, Fibularis (Peroneus)Longus, Soleus, Gluteus maximus, Gluteus medius, Gluteus minimus,Hamstrings: Biceps Femoris: Long Head, Hamstrings: Biceps Femoris: ShortHead, Hamstrings: Semitendinosus, Hamstrings: Semimembranosus, Tensorfasciae latae, Pectineus, and/or Tibialis anterior.

In some embodiments, muscles of the foreleg and foot include, but arenot limited to, Extensor digitorum longus, Extensor hallucis longus,peroneus brevis, plantaris, Tibialis posterior, Flexor hallucis longus,extensor digitorum brevis, extensor hallucis brevis, Abductor hallucis,flexor hallucis brevis, Abductor digiti minimi, flexor digiti minimi,opponens digiti minimi, extensor digitorum brevis, lumbricales of thefoot, Quadratus plantae or flexor accessorius, flexor digitorum brevis,dorsal interossei, and/or plantar interossei.

Exemplary muscle targets are summarized in Table 1.

TABLE 1 ORBICULARIS OCULI Intraocular: ciliary, iris dilator, irissphincter Ear: auriculares, temporoparietalis, stapedius, tensor tympaniNose: procerus, nasalis, dilator naris, depressor septi nasi, levatorlabii superioris alaeque nasi Mouth: levator anguli oris, depressoranguli oris, orbicularis oris Buccinator Zygomaticus Major PlatysmaLevator Labii and Minor Superioris Depressor Labii Risorius MentalisCorrugator Inferioris Supercilii Anconeus Pronator teres SupinatorBrachialis MUSCLES OF MASTICATON Masseter Temporalis Medial PterygoidLateral Pterygoid MUSCLES OF THE TONGUE AND NECK GenioglossusStyloglossus Palatoglossus Hyoglossus Digastric Stylohyoid MylohyoidGeniohyoid Omohyoid Sternohyoid Sternothyroid ThyrohyoidSternocleidomastoid Anterior Scalene Middle Scalene Posterior ScaleneMUSCLES OF THE THORAX, PECTORAL GIRDLE AND ARMS Subclavius Pectoralismajor Pectoralis minor Rectus abdominis External abdominal Internalabdominal Transversus Diaphragm oblique oblique Abdominis ExternalIntercostals Internal Intercostals Serratus Anterior Trapezius LevatorScapulae Rhomboideus Major Rhomboideus Minor Latissimus dorsi Deltoidsubscapularis supraspinatus infraspinatus Teres major Teres minorCoracobrachialis ARM AND SHOULDER Biceps brachii- Biceps brachii-ShortTriceps brachii- Triceps brachii- Long Head Head Long Head Lateral HeadTriceps brachii- Anconeus Pronator teres Supinator Medial HeadBrachialis FOREARM MUSCLES: Ventral and Dorsal Brachioradialis Flexorcarpi Flexor carpi Palmaris longus radialis ulnaris Extensor carpiExtensor carpi Extensor carpi Extensor digitorum ulnaris radialis longusradialis brevis Extensor digiti erector spinae: erector spinae: erectorspinae: minimi cervicalis spinalis longissimus erector spinae:iliocostalis Intrinsic Muscles of the Hand: thenar, abductor pollicisbrevis, flexor pollicis brevis, and the opponens pollicis IntrinsicMuscles of the Hand: hypothenar, abductor digiti minimi, the flexordigiti minimi brevis, and the opponens digiti minimi Intrinsic Musclesof the Hand: palmar interossei, dorsal interossei and lumbricals MUSCLESOF THE PELVIC GIRDLE AND THE LEGS Iliopsoas: Psoas Iliopsoas: Iliacusquadratus femoris Adductor longus Major Adductor brevis Adductor magnusGracilis Sartorius Quadriceps femoris: Quadriceps femoris: Quadricepsfemoris: Quadriceps femoris: rectus femoris vastus lateralis vastusmedialis vastus intermedius Gastrocnemius Fibularis (Peroneus) SoleusGluteus maximus Longus Gluteus medius Gluteus minimus Hamstrings: BicepsHamstrings: Biceps Femoris: Long Head Femoris: Short Head Hamstrings:Hamstrings: Tensor fasciae latae Pectineus SemitendinosusSemimembranosus Tibialis anterior MUSCLES OF THE FORELEG AND FOOTExtensor digitorum Extensor hallucis peroneus brevis plantaris longuslongus Tibialis posterior Flexor hallucis extensor digitorum extensorhallucis longus brevis brevis Abductor hallucis flexor hallucis Abductordigiti flexor digiti brevis minimi minimi opponens digiti extensordigitorum lumbricales of the Quadratus plantae minimi brevis foot orflexor accessorius Flexor digitorum dorsal interossei plantar interosseibrevis

Muscular Dystrophy

Muscular dystrophies are a group of inherited disorders that causedegeneration of muscle, leading to weak and impaired movements. Acentral feature of all muscular dystrophies is that they are progressivein nature. Muscular dystrophies include, but are not limited to:Duchenne muscular dystrophy (DMD), Becker muscular dystrophy,Emery-Dreifuss muscular dystrophy, facioscapulohumeral musculardystrophy, limb-girdle muscular dystrophies, and myotonic dystrophyTypes 1 and 2, including the congenital form of Myotonic dystrophyType 1. Symptoms may vary by type of muscular dystrophy with some or allmuscles being affected. Exemplary symptoms of muscular dystrophiesinclude delayed development of muscle motor skills, difficulty using oneor more muscle groups, difficulty swallowing, speaking or eating,drooling, eyelid drooping, frequent falling, loss of strength in amuscle or group of muscles as an adult, loss in muscle size, problemswalking due to weakness or altered biomechanics of the body, musclehypertrophy, muscle pseudohypertrophy, fatty infiltration of muscle,replacement of muscle with non-contractile tissue (e.g., musclefibrosis), muscle necrosis, and/or cognitive or behavioralimpairment/mental retardation.

While there are no known cures for muscular dystrophies, severalsupportive treatments are used which include both symptomatic anddisease modifying therapies. Corticosteroids, physical therapy, orthoticdevices, wheelchairs, or other assistive medical devices for ADLs andpulmonary function are commonly used in muscular dystrophies. Cardiacpacemakers are used to prevent sudden death from cardiac arrhythmias inMyotonic dystrophy. Anti-myotonic agents which improve the symptoms ofmyotonia (inability to relax) include mexilitine, and in some casesphenytoin, procainamide and quinine.

Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a recessive X-linked form ofmuscular dystrophy which results in muscle degeneration and eventualdeath. DMD is characterized by weakness in the proximal muscles,abnormal gait, psuedohypertrophy in the gastrocnemius (calf) muscles,and elevated creatine kinase (CK). Many DMD patients are diagnosedaround the age of 5, when symptoms/signs typically become more obvious.Affected individuals typically stop walking around age 10-13 and die inor before their mid to late 20's due to cardiorespiratory dysfunction.

The disorder DMD is caused by a mutation in the dystrophin gene, locatedon the human X chromosome, which codes for the protein dystrophin, animportant structural component within muscle tissue that providesstructural stability to the dystroglycan complex (DGC) of the cellmembrane. Dystrophin links the internal cytoplasmic actin filamentnetwork and extracellular matrix, providing physical strength to musclefibers. Accordingly, alteration or absence of dystrophin results inabnormal sarcolemmal membrane tearing and necrosis of muscle fibers.While persons of both sexes can carry the mutation, females rarelyexhibit severe signs of the disease.

A main symptom of DMD is muscle weakness associated with muscle wastingwith the voluntary muscles being first affected typically, especiallyaffecting the muscles of the hips, pelvic area, thighs, shoulders, andcalf muscles. Muscle weakness also occurs in the arms, neck, and otherareas. Calves are often enlarged. Signs and symptoms usually appearbefore age 6 and may appear as early as infancy. Other physical symptomsinclude, but are not limited to, delayed ability to walk independently,progressive difficulty in walking, stepping, or running, and eventualloss of ability to walk (usually by the age of 15); frequent falls;fatigue; difficulty with motor skills (running, hopping, jumping);increased lumbar lordosis, leading to shortening of the hip-flexormuscles; contractures of achilles tendon and hamstrings impairingfunctionality because the muscle fibers shorten and fibrosis occurs inconnective tissue; muscle fiber deformities; pseudohypertrophy(enlargement) of tongue and calf muscles caused by replacement of muscletissue by fat and connective tissue; higher risk of neurobehavioraldisorders (e.g., ADHD), learning disorders (dyslexia), andnon-progressive weaknesses in specific cognitive skills (in particularshort-term verbal memory); skeletal deformities (including scoliosis insome cases).

Recombinant Follistatin Proteins

As used herein, recombinant follistatin proteins suitable for thepresent invention include any wild-type and modified follistatinproteins (e.g., follistatin proteins with amino acid mutations,deletions, insertions, and/or fusion proteins) that retain substantialfollistatin biological activity. Typically, a recombinant follistatinprotein is produced using recombinant technology. However, follistatinproteins (wild-type or modified) purified from natural resources orsynthesized chemically can be used according to the present invention.Typically, a suitable recombinant follistatin protein has an in vivohalf-life of or greater than about 12 hours, 18 hours, 24 hours, 36hours, 2 days, 2.5 days, 3 days, 3.5 days, 4 days, 4.5 days, 5 days, 5.5days, 6 days, 6.5 days, 7 days, 7.5 days, 8 days, 8.5 days, 9 days, 9.5days, or 10 days. In some embodiments, a recombinant follistatin proteinhas an in vivo half-life of between 0.5 and 10 days, between 1 day and10 days, between 1 day and 9 days, between 1 day and 8 days, between 1day and 7 days, between 1 day and 6 days, between 1 day and 5 days,between 1 day and 4 days, between 1 day and 3 days, between 2 days and10 days, between 2 days and 9 days, between 2 days and 8 days, between 2days and 7 days, between 2 days and 6 days, between 2 days and 5 days,between 2 days and 4 days, between 2 day and 3 days, between 2.5 daysand 10 days, between 2.5 days and 9 days, between 2.5 days and 8 days,between 2.5 days and 7 days, between 2.5 days and 6 days, between 2.5days and 5 days, between 2.5 days and 4 days, between 3 days and 10days, between 3 days and 9 days, between 3 days and 8 days, between 3days and 7 days, between 3 days and 6 days, between 3 days and 5 days,between 3 days and 4 days, between 3.5 days and 10 days, between 3.5days and 9 days, between 3.5 days and 8 days, between 3.5 days and 7days, between 3.5 days and 6 days, between 3.5 days and 5 days, between3.5 days and 4 days, between 4 days and 10 days, between 4 days and 9days, between 4 days and 8 days, between 4 days and 7 days, between 4days and 6 days, between 4 days and 5 days, between 4.5 days and 10days, between 4.5 days and 9 days, between 4.5 days and 8 days, between4.5 days and 7 days, between 4.5 days and 6 days, between 4.5 days and 5days, between 5 days and 10 days, between 5 days and 9 days, between 5days and 8 days, between 5 days and 7 days, between 5 days and 6 days,between 5.5 days and 10 days, between 5.5 days and 9 days, between 5.5days and 8 days, between 5.5 days and 7 days, between 5.5 days and 6days, between 6 days and 10 days, between 7 days and 10 days, between 8days and 10 days, between 9 days and 10 days.

Follistatin (FS) was first isolated from follicular fluid, as a proteinfactor capable of suppressing pituitary cell follicle stimulatinghormone (FSH) secretion. FS exerts its influence over FSH at least inpart through the binding and neutralization of activin.

There are at least two isoforms of FS: FS288 and FS315, created throughalternative splicing at the C-terminus. The 288-amino acid isoform has adistinctive structure comprised of a 63 amino acid N-terminal regioncontaining hydrophobic residues important for activin binding, with themajor portion of the protein (residues 64-288) comprising three10-cysteine FS domains of approximately 73-75 amino acids each. These10-cysteine domains, from N-terminus to C-terminus, are referred to asdomain 1, domain 2 and domain 3, respectively. The FS315 isoform iscreated through an acidic extension of the C-terminus encoded by anextra exon. FS288 tends to be tissue-bound due to the presence of aheparin binding domain, while FS315 tends to be a circulating form,potentially because the heparin binding domain is masked by the extendedC-terminus.

It has been shown that FS inhibits both myostatin and activin in vitroand that this inhibition can lead to hypertrophy in vivo in mice (Lee etal., Regulation of Muscle Mass by Follistatin and Activins, (2010), MOL.ENDOCRINOL., 24(10): 1998-2008; Gilson et al., Follistatin InducesMuscle Hypertrophy Through Satellite Cell Proliferation and Inhibitionof Both Myostatin and Activin, (2009), J. PHYSIOL. ENDOCRINOL.,297(1):E157-E164). Without wishing to be held to a particular theory,this observed effect may be at least partially due to FS preventingactivation of the Smad2/3 pathway by myostatin and activin. Activationof the Smad2/3 pathway has been shown to result in negative regulationof muscle growth (Zhu et al., Follistatin Improves Skeletal MuscleHealing After Injury and Disease Through an Interaction with MuscleRegeneration, Angiogenesis, and Fibrosis, (2011), MUSCULOSKELETALPATHOLOGY, 179(2):915-930).

The amino acid sequences of a typical wild-type or naturally-occurringhuman FS315 and FS288 protein are shown in Table 2.

TABLE 2 Exemplary Human Follistatin Isoforms FS315GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEW (SEQ ID NO: 1) FS288GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCN (SEQ ID NO: 12)

Thus, in some embodiments, a recombinant follistatin protein suitablefor the present invention is human FS315 (SEQ ID NO:1). As disclosedherein, SEQ ID NO:1 represents the canonical amino acid sequence for thehuman follistatin protein. In some embodiments, a follistatin proteinmay be a splice isoform such as FS 288 (SEQ ID NO:12). In someembodiments, a suitable recombinant follistatin protein may be ahomologue or an analogue of a wild-type or naturally-occurring protein.For example, a homologue or an analogue of human wild-type ornaturally-occurring follistatin protein may contain one or more aminoacid or domain substitutions, deletions, and/or insertions as comparedto a wild-type or naturally-occurring follistatin protein (e.g., SEQ IDNO:1), while retaining substantial follistatin protein activity. Thus,in some embodiments, a recombinant follistatin protein suitable for thepresent invention is substantially homologous to human FS315 follistatinprotein (SEQ ID NO:1). In some embodiments, a recombinant follistatinprotein suitable for the present invention has an amino acid sequence atleast 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%,95%, 96%, 97%, 98%, 99% or more homologous to SEQ ID NO:1. In someembodiments, a recombinant follistatin protein suitable for the presentinvention is substantially identical to human FS315 follistatin protein(SEQ ID NO:1). In some embodiments, a recombinant follistatin proteinsuitable for the present invention has an amino acid sequence at least50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99% or more identical to SEQ ID NO:1.

Homologues or analogues of human follistatin proteins can be preparedaccording to methods for altering polypeptide sequence known to one ofordinary skill in the art such as are found in references that compilesuch methods. As will be appreciated by those of ordinary skill in theart, two sequences are generally considered to be “substantiallyhomologous” if they contain homologous residues in correspondingpositions. Homologous residues may be identical residues. Alternatively,homologous residues may be non-identical residues will appropriatelysimilar structural and/or functional characteristics. For example, as iswell known by those of ordinary skill in the art, certain amino acidsare typically classified as “hydrophobic” or “hydrophilic” amino acids.,and/or as having “polar” or “non-polar” side chains Substitution of oneamino acid for another of the same type may often be considered a“homologous” substitution. In some embodiments, conservativesubstitutions of amino acids include substitutions made among aminoacids within the following groups: (a) M, I, L, V; (b) F, Y, W; (c) K,R, H; (d) A, G; (e) S, T; (f) Q, N; and (g) E, D. In some embodiments, a“conservative amino acid substitution” refers to an amino acidsubstitution that does not alter the relative charge or sizecharacteristics of the protein in which the amino acid substitution ismade.

As is well known in this art, amino acid or nucleic acid sequences maybe compared using any of a variety of algorithms, including thoseavailable in commercial computer programs such as BLASTN for nucleotidesequences and BLASTP, gapped BLAST, and PSI-BLAST for amino acidsequences. Exemplary such programs are described in Altschul, et al.,Basic local alignment search tool, J. Mol. Biol., 215(3): 403-410, 1990;Altschul, et al., Methods in Enzymology; Altschul, et al., “Gapped BLASTand PSI-BLAST: a new generation of protein database search programs”,Nucleic Acids Res. 25:3389-3402, 1997; Baxevanis, et al.,Bioinformatics: A Practical Guide to the Analysis of Genes and Proteins,Wiley, 1998; and Misener, et al., (eds.), Bioinformatics Methods andProtocols (Methods in Molecular Biology, Vol. 132), Humana Press, 1999.In addition to identifying homologous sequences, the programs mentionedabove typically provide an indication of the degree of homology.

In some embodiments, a recombinant follistatin protein suitable for thepresent invention contains one or more amino acid deletions, insertionsor replacement as compared to a wild-type human follistatin protein. Forexample, a suitable recombinant follistatin protein may contain aminoacid substitutions at positions corresponding to Y185 and/or L191, ofSEQ ID NO:1.

Domain Deletion Variants

In some embodiments, a recombinant follistatin protein suitable for thepresent invention contains one or more domain deletions, insertions orreplacement (e.g., domain swapping) as compared to a wild-type humanfollistatin protein. For example, a recombinant follistatin proteinsuitable for the present invention may contain a deletion, insertionand/or replacement of amino acid sequences corresponding to domain 1, 2and/or 3. In certain embodiments, a recombinant follistatin proteincomprises a deletion of amino acids residues 212-288 of SEQ ID NO:1(which corresponds to domain 3), as shown below:

(SEQ ID NO: 2) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCISISEDTEEEEEDEDQDYSFPISSILEW.

It is contemplated that a suitable recombinant follistatin protein maybe a homologue or an analogue of a suitable domain deletion variant,containing one or more amino acid substitutions, deletions, and/orinsertions as compared to the suitable follistatin domain deletionvariant (e.g., SEQ ID NO:2), while retaining substantial follistatinprotein activity. Thus, in some embodiments, a recombinant follistatinprotein suitable for the present invention has an amino acid sequence atleast 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%,95%, 96%, 97%, 98%, 99% or more homologous or identical to SEQ ID NO:2.

Follistatin Fusion Proteins

It is contemplated that a suitable recombinant follistatin protein canbe in a fusion protein configuration. For example, a recombinantfollistatin protein suitable for the present invention may be a fusionprotein between a follistatin domain and another domain or moiety thattypically can facilitate a therapeutic effect of follistatin by, forexample, enhancing or increasing stability, potency and/or delivery offollistatin protein, or reducing or eliminating immunogenicity,clearance, or toxicity. Such suitable domains or moieties for afollistatin fusion protein include but are not limited to Fc domain,XTEN domain.

Fc Domain

In some embodiments, a suitable recombinant follistatin protein containsan Fc domain or a portion thereof that binds to the FcRn receptor. As anon-limiting example, a suitable Fc domain may be derived from animmunoglobulin subclass such as IgG. In some embodiments, a suitable Fcdomain is derived from IgG1, IgG2, IgG3, or IgG4. In some embodiments, asuitable Fc domain is derived from IgM, IgA, IgD, or IgE. Particularlysuitable Fc domains include those derived from human or humanizedantibodies. In some embodiments, a suitable Fc domain is a modified Fcportion, such as a modified human Fc portion.

In some embodiments, a suitable Fc domain comprises an amino acidsequence shown below

(SEQ ID NO: 3) EPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK, or (SEQ ID NO: 4)KTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK; or (SEQ ID NO: 14)DKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK.

In some embodiments, a suitable Fc domain comprises an amino acidsequence at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99% or more homologous or identical to SEQID NO: 3, SEQ ID NO: 4, or SEQ ID NO: 14.

It is contemplated that improved binding between Fc domain and the FcRnreceptor results in prolonged serum half-life. Thus, in someembodiments, a suitable Fc domain comprises one or more amino acidmutations that lead to improved binding to FcRn. Various mutationswithin the Fc domain that effect improved binding to FcRn are known inthe art and can be adapted to practice the present invention. In someembodiments, a suitable Fc domain comprises one or more mutations at oneor more positions corresponding to Thr 250, Met 252, Ser 254, Thr 256,Thr 307, Glu 380, Met 428, His 433 and/or Asn 434 of human IgG1.

For example, a suitable Fc domain may contain mutations of H433K(His433Lys) and/or N434F (Asn434Phe). As a non-limiting example, asuitable Fc domain may contain mutations H433K (His433Lys) and N434F(Asn434Phe). An exemplary Fc domain sequence incorporating the mutationsis shown below:

(SEQ ID NO: 15) DKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSR WQQGNVFSCSVMHEAL KFHYTQKSLSLSPGK.

Additional amino acid substitutions that can be included in a Fc domaininclude those described in, e.g., U.S. Pat. Nos. 6,277,375; 8,012,476;and 8,163,881, which are incorporated herein by reference.

Linker or Spacer

A follistatin domain may be directly or indirectly linked to an Fcdomain. In some embodiments, a suitable recombinant follistatin proteincontains a linker or spacer that joins a follistatin domain and an Fcdomain. An amino acid linker or spacer is generally designed to beflexible or to interpose a structure, such as an alpha-helix, betweenthe two protein moieties. A linker or spacer can be relatively short, orcan be longer. Typically, a linker or spacer contains for example 3-100(e.g., 5-100, 10-100, 20-100 30-100, 40-100, 50-100, 60-100, 70-100,80-100, 90-100, 5-55, 10-50, 10-45, 10-40, 10-35, 10-30, 10-25, 10-20)amino acids in length. In some embodiments, a linker or spacer is equalto or longer than 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 amino acids inlength. Typically, a longer linker may decrease steric hindrance. Insome embodiments, a linker will comprise a mixture of glycine and serineresidues. In some embodiments, the linker may additionally comprisethreonine, proline and/or alanine residues. Thus, in some embodiments,the linker comprises between 10-100, 10-90, 10-80, 10-70, 10-60, 10-50,10-40, 10-30, 10-20, 10-15 amino acids. In some embodiments, the linkercomprises at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, or 95 amino acids. In some embodiments, the linker isnot a linker consisting of ALEVLFQGP (SEQ ID NO: 18).

As non-limiting examples, linkers or spacers suitable for the presentinvention include but are not limited to: GAPGGGGGAAAAAGGGGGGAP (GAGlinker, SEQ ID NO: 5); GAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAP (GAG2linker, SEQ ID NO:6); andGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGG GAP (GAG3 linker,SEQ ID NO:7).

Suitable linkers or spacers also include those having an amino acidsequence at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, 99% or more homologous or identical to theabove exemplary linkers, e.g., GAG linker (SEQ ID NO:5), GAG2 linker(SEQ ID NO:6), or GAG3 linker (SEQ ID NO:7). Additional linkers suitablefor use with some embodiments may be found in US20120232021, filed onMar. 2, 2012, the disclosure of which is hereby incorporated byreference in its entirety,

In some embodiments, a linker is provided that associates thefollistatin polypeptide with the Fc domain without substantiallyaffecting the ability of the follistatin polypeptide to bind to any ofits cognate ligands (e.g., activin, myostatin, heparin, etc.). In someembodiments, a linker is provided such that the binding of a follistatinpeptide to heparin is not altered as compared to the follistatinpolypeptide alone. For example, in some embodiments, a follistatinpolypeptide is a FS315 polypeptide, which normally does not bind heparinunless it is associated with activin. In some such embodiments, a linkeris provided that does not result in increased heparin binding of theFS315 polypeptide as compared to the FS315 polypeptide alone.

Exemplary Follistatin Fusion Proteins

In particular embodiments, a suitable recombinant follistatin fusionprotein includes a follistatin polypeptide, an Fc domain, and a linkerthat associates the follistatin polypeptide with the Fc domain, whereinthe follistatin polypeptide comprises an amino acid sequence at least50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%,96%, 97%, 98%, 99% or 100% identical to the wild-type human FS315protein (SEQ ID NO:1) or a domain 3 deleted FS315 protein (SEQ ID NO:2).Typically, a suitable recombinant follistatin fusion protein is capableof binding to activin and myostatin. In some embodiments, a suitablerecombinant follistatin fusion protein has an in vivo half-life rangingfrom about 0.5-6 days (e.g., about 0.5-5.5 days, about 0.5-5 days, about1-5 days, about 1.5-5 days, about 1.5-4.5 days, about 1.5-4.0 days,about 1.5-3.5 days, about 1.5-3 days, about 1.5-2.5 days, about 2-6days, about 2-5.5 days, about 2-5 days, about 2-4.5 days, about 2-4days, about 2-3.5 days, about 2-3 days). In some embodiments, a suitablerecombinant follistatin fusion protein has an in vivo half-life rangingfrom about 2-10 days (e.g., ranging from about 2.5-10 days, from about3-10 days, from about 3.5-10 days, from about 4-10 days, from about4.5-10 days, from about 5-10 days, from about 3-8 days, from about 3.5-8days, from about 4-8 days, from about 4.5-8 days, from about 5-8 days,from about 3-6 days, from about 3.5-6 days, from about 4-6 days, fromabout 4.5-6 days, from about 5-6 days).

As non-limiting examples, suitable follistatin Fc fusion proteins mayhave an amino acid sequence shown below:

(SEQ ID NO: 9) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEA LHNHYTQKSLSLSPGK, or(SEQ ID NO: 9) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEA LHNHYTQKSLSLSPGK.

As other non-limiting examples, suitable follistatin Fc fusion proteinsmay have an amino acid sequence shown below:

(SEQ ID NO: 11) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCISISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK, or (SEQ ID NO: 11)GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCISISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK.

As yet other non-limiting examples, suitable follistatin Fc fusionproteins may have an amino acid sequence shown below:

(SEQ ID NO: 16) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHY TQKSLSLSPGK Or(SEQ ID NO: 17) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALKFHY TQKSLSLSPGK

In some embodiments, a suitable recombinant follistatin Fc fusionprotein has an amino acid sequence at least 50%, 55%, 60%, 65%, 70%,75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or morehomologous or identical to SEQ ID NO:8, 9, 10, 11, 16 or 17.

It is contemplated that a follistatin-Fc fusion protein may be providedin various configurations including homodimeric or monomericconfigurations. For example, a suitable homodimeric configuration may bedesigned to have the C-terminal end of fusion partner (e.g., afollistatin polypeptide plus linker) attached to the N-terminal end ofboth Fc polypeptide strands. A suitable monomeric configuration may bedesigned to have the C-terminal end of fusion partner (e.g., afollistatin polypeptide plus linker) fused to one Fc dimer. A monomericconfiguration may decrease steric hindrance.

As used herein, “percent (%) amino acid sequence identity” with respectto a reference protein sequence (e.g., a reference follistatin proteinsequence) identified herein is defined as the percentage of amino acidresidues in a candidate sequence that are identical with the amino acidresidues in the reference sequence, after aligning the sequences andintroducing gaps, if necessary, to achieve the maximum percent sequenceidentity, and not considering any conservative substitutions as part ofthe sequence identity. Alignment for purposes of determining percentamino acid sequence identity can be achieved in various ways that arewithin the skill in the art, for instance, using publicly availablecomputer software such as BLAST, ALIGN or Megalign (DNASTAR) software.Those skilled in the art can determine appropriate parameters formeasuring alignment, including any algorithms needed to achieve maximalalignment over the full length of the sequences being compared.Preferably, the WU-BLAST-2 software is used to determine amino acidsequence identity (Altschul et al., Methods in Enzymology 266, 460-480(1996); http://blast.wustl/edu/blast/README.html). WU-BLAST-2 usesseveral search parameters, most of which are set to the default values.The adjustable parameters are set with the following values: overlapspan=1, overlap fraction=0.125, world threshold (T)=11. HSP score (S)and HSP S2 parameters are dynamic values and are established by theprogram itself, depending upon the composition of the particularsequence, however, the minimum values may be adjusted and are set asindicated above.

Production of Recombinant Follistatin Proteins

A recombinant follistatin protein suitable for the present invention maybe produced by any available means. For example, a recombinantfollistatin protein may be recombinantly produced by utilizing a hostcell system engineered to express a recombinant follistatinprotein-encoding nucleic acid. Alternatively or additionally, arecombinant follistatin protein may be produced by activating endogenousgenes. Alternatively or additionally, a recombinant follistatin proteinmay be partially or fully prepared by chemical synthesis.

Where proteins are recombinantly produced, any expression system can beused. To give but a few examples, known expression systems include, forexample, E. coli, egg, baculovirus, plant, yeast, or mammalian cells.

In some embodiments, recombinant follistatin proteins suitable for thepresent invention are produced in mammalian cells. Non-limiting examplesof mammalian cells that may be used in accordance with the presentinvention include BALB/c mouse myeloma line (NSO/l, ECACC No: 85110503);human retinoblasts (PER.C6, CruCell, Leiden, The Netherlands); monkeykidney CV1 line transformed by SV40 (COS-7, ATCC CRL 1651); humanembryonic kidney line (HEK293 or 293 cells subcloned for growth insuspension culture, Graham et al., J. Gen Virol., 36:59, 1977); humanfibrosarcoma cell line (e.g., HT1080); baby hamster kidney cells (BHK21,ATCC CCL 10); Chinese hamster ovary cells +/−DHFR (CHO, Urlaub andChasin, Proc. Natl. Acad. Sci. USA, 77:4216, 1980); mouse sertoli cells(TM4, Mather, Biol. Reprod., 23:243-251, 1980); monkey kidney cells (CV1ATCC CCL 70); African green monkey kidney cells (VERO-76, ATCC CRL-1587); human cervical carcinoma cells (HeLa, ATCC CCL 2); canine kidneycells (MDCK, ATCC CCL 34); buffalo rat liver cells (BRL 3A, ATCC CRL1442); human lung cells (W138, ATCC CCL 75); human liver cells (Hep G2,HB 8065); mouse mammary tumor (MMT 060562, ATCC CCL51); TRI cells(Mather et al., Annals N.Y. Acad. Sci., 383:44-68, 1982); MRC 5 cells;FS4 cells; and a human hepatoma line (Hep G2).

In some embodiments, the present invention provides recombinantfollistatin proteins produced from human cells. In some embodiments, thepresent invention provides recombinant follistatin proteins producedfrom CHO cells or HT1080 cells.

Typically, cells that are engineered to express a recombinantfollistatin protein may comprise a transgene that encodes a recombinantfollistatin protein described herein. It should be appreciated that thenucleic acids encoding recombinant follistatin protein may containregulatory sequences, gene control sequences, promoters, non-codingsequences and/or other appropriate sequences for expressing therecombinant follistatin protein. Typically, the coding region isoperably linked with one or more of these nucleic acid components.

The coding region of a transgene may include one or more silentmutations to optimize codon usage for a particular cell type. Forexample, the codons of a follistatin transgene may be optimized forexpression in a vertebrate cell. In some embodiments, the codons of afollistatin transgene may be optimized for expression in a mammaliancell. In some embodiments, the codons of a follistatin transgene may beoptimized for expression in a human cell.

Pharmaceutical Composition and Administration

The present invention further provides a pharmaceutical compositioncontaining a recombinant follistatin protein described herein and aphysiologically acceptable carrier or excipient.

Suitable pharmaceutically acceptable carriers include but are notlimited to water, salt solutions (e.g., NaCl), saline, buffered saline,alcohols, glycerol, ethanol, gum arabic, vegetable oils, benzylalcohols, polyethylene glycols, gelatin, carbohydrates such as lactose,amylose or starch, sugars such as mannitol, sucrose, or others,dextrose, magnesium stearate, talc, silicic acid, viscous paraffin,perfume oil, fatty acid esters, hydroxymethylcellulose, polyvinylpyrolidone, etc., as well as combinations thereof. The pharmaceuticalpreparations can, if desired, be mixed with auxiliary agents (e.g.,lubricants, preservatives, stabilizers, wetting agents, emulsifiers,salts for influencing osmotic pressure, buffers, coloring, flavoringand/or aromatic substances and the like) which do not deleteriouslyreact with the active compounds or interference with their activity. Ina preferred embodiment, a water-soluble carrier suitable for intravenousadministration is used.

A suitable pharmaceutical composition or medicament, if desired, canalso contain minor amounts of wetting or emulsifying agents, or pHbuffering agents. A composition can be a liquid solution, suspension,emulsion, tablet, pill, capsule, sustained release formulation, orpowder. A composition can also be formulated as a suppository, withtraditional binders and carriers such as triglycerides. Oralformulations can include standard carriers such as pharmaceutical gradesof mannitol, lactose, starch, magnesium stearate, polyvinyl pyrrolidone,sodium saccharine, cellulose, magnesium carbonate, etc.

A pharmaceutical composition or medicament can be formulated inaccordance with the routine procedures as a pharmaceutical compositionadapted for administration to human beings. For example, in someembodiments, a composition for intravenous administration typically is asolution in sterile isotonic aqueous buffer. Where necessary, thecomposition may also include a solubilizing agent and a local anestheticto ease pain at the site of the injection. Generally, the ingredientsare supplied either separately or mixed together in unit dosage form,for example, as a dry lyophilized powder or water free concentrate in ahermetically sealed container such as an ampule or sachette indicatingthe quantity of active agent. Where the composition is to beadministered by infusion, it can be dispensed with an infusion bottlecontaining sterile pharmaceutical grade water, saline or dextrose/water.Where the composition is administered by injection, an ampule of sterilewater for injection or saline can be provided so that the ingredientsmay be mixed prior to administration.

A recombinant follistatin protein described herein can be formulated asneutral or salt forms. Pharmaceutically acceptable salts include thoseformed with free amino groups such as those derived from hydrochloric,phosphoric, acetic, oxalic, tartaric acids, etc., and those formed withfree carboxyl groups such as those derived from sodium, potassium,ammonium, calcium, ferric hydroxides, isopropylamine, triethylamine,2-ethylamino ethanol, histidine, procaine, etc.

Routes of Administration

A recombinant follistatin protein described herein (or a composition ormedicament containing a recombinant follistatin protein describedherein) is administered by any appropriate route. In some embodiments, arecombinant follistatin protein or a pharmaceutical compositioncontaining the same is administered systemically. Systemicadministration may be intravenous, intradermal, inhalation, transdermal(topical), intraocular, intramuscular, subcutaneous, intramuscular, oraland/or transmucosal administration. In some embodiments, a recombinantfollistatin protein or a pharmaceutical composition containing the sameis administered subcutaneously. As used herein, the term “subcutaneoustissue”, is defined as a layer of loose, irregular connective tissueimmediately beneath the skin. For example, the subcutaneousadministration may be performed by injecting a composition into areasincluding, but not limited to, the thigh region, abdominal region,gluteal region, or scapular region. In some embodiments, a recombinantfollistatin protein or a pharmaceutical composition containing the sameis administered intravenously. In some embodiments, a recombinantfollistatin protein or a pharmaceutical composition containing the sameis administered orally. More than one route can be used concurrently, ifdesired.

In some embodiments, administration results only in a localized effectin an individual, while in other embodiments, administration results ineffects throughout multiple portions of an individual, for example,systemic effects. Typically, administration results in delivery of arecombinant follistatin protein to one or more target tissues. In someembodiments, the recombinant follistatin protein is delivered to one ormore target tissues including, but not limited to, heart, brain, spinalcord, striated muscle (e.g., skeletal muscle), smooth muscle, kidney,liver, lung, and/or spleen. In some embodiments, the recombinantfollistatin protein is delivered to the heart. In some embodiments, therecombinant follistatin protein is delivered to striated muscle, inparticular, skeletal muscle. In some embodiments, the recombinantfollistatin protein is delivered to triceps, tibialis anterior, soleus,gastrocnemius, biceps, trapezius, deltoids, quadriceps, and/ordiaphragm.

Dosage Forms and Dosing Regimen

In some embodiments, a composition is administered in a therapeuticallyeffective amount and/or according to a dosing regimen that is correlatedwith a particular desired outcome (e.g., with treating or reducing riskfor a muscular dystrophy, such as Duchenne muscular dystrophy).

Particular doses or amounts to be administered in accordance with thepresent invention may vary, for example, depending on the nature and/orextent of the desired outcome, on particulars of route and/or timing ofadministration, and/or on one or more characteristics (e.g., weight,age, personal history, genetic characteristic, lifestyle parameter,severity of cardiac defect and/or level of risk of cardiac defect, etc.,or combinations thereof). Such doses or amounts can be determined bythose of ordinary skill. In some embodiments, an appropriate dose oramount is determined in accordance with standard clinical techniques.Alternatively or additionally, in some embodiments, an appropriate doseor amount is determined through use of one or more in vitro or in vivoassays to help identify desirable or optimal dosage ranges or amounts tobe administered.

In various embodiments, a recombinant follistatin protein isadministered at a therapeutically effective amount. Generally, atherapeutically effective amount is sufficient to achieve a meaningfulbenefit to the subject (e.g., treating, modulating, curing, preventingand/or ameliorating the underlying disease or condition). In someparticular embodiments, appropriate doses or amounts to be administeredmay be extrapolated from dose-response curves derived from in vitro oranimal model test systems.

In some embodiments, a provided composition is provided as apharmaceutical formulation. In some embodiments, a pharmaceuticalformulation is or comprises a unit dose amount for administration inaccordance with a dosing regimen correlated with achievement of thereduced incidence or risk of a muscular dystrophy, such as Duchennemuscular dystrophy.

In some embodiments, a formulation comprising a recombinant follistatinprotein described herein administered as a single dose. In someembodiments, a formulation comprising a recombinant follistatin proteindescribed herein is administered at regular intervals. Administration atan “interval,” as used herein, indicates that the therapeuticallyeffective amount is administered periodically (as distinguished from aone-time dose). The interval can be determined by standard clinicaltechniques. In some embodiments, a formulation comprising a recombinantfollistatin protein described herein is administered bimonthly, monthly,twice monthly, triweekly, biweekly, weekly, twice weekly, thrice weekly,daily, twice daily, or every six hours. The administration interval fora single individual need not be a fixed interval, but can be varied overtime, depending on the needs of the individual.

As used herein, the term “bimonthly” means administration once per twomonths (i.e., once every two months); the term “monthly” meansadministration once per month; the term “triweekly” means administrationonce per three weeks (i.e., once every three weeks); the term “biweekly”means administration once per two weeks (i.e., once every two weeks);the term “weekly” means administration once per week; and the term“daily” means administration once per day.

In some embodiments, a formulation comprising a recombinant follistatinprotein described herein is administered at regular intervalsindefinitely. In some embodiments, a formulation comprising arecombinant follistatin protein described herein is administered atregular intervals for a defined period.

Combination Therapy

In some embodiments, a recombinant follistatin protein is administeredin combination with one or more known therapeutic agents (e.g.,corticosteroids) currently used for treatment of a muscular dystrophy.In some embodiments, the known therapeutic agent(s) is/are administeredaccording to its standard or approved dosing regimen and/or schedule. Insome embodiments, the known therapeutic agent(s) is/are administeredaccording to a regimen that is altered as compared with its standard orapproved dosing regimen and/or schedule. In some embodiments, such analtered regimen differs from the standard or approved dosing regimen inthat one or more unit doses is altered (e.g., reduced or increased) inamount, and/or in that dosing is altered in frequency (e.g., in that oneor more intervals between unit doses is expanded, resulting in lowerfrequency, or is reduced, resulting in higher frequency).

EXAMPLES Example 1. Follistatin Targets Myostatin and ActivinSpecifically

This example illustrates Follistatin binding to target and non-targetligands to evaluate safety of Follistatin as a protein therapeutic fortreating DMD. Without wishing to be bound by theory, it is contemplatedthat activation of Smad2/3 pathway by myostatin and activin leads toinhibition of myogenic protein expression. As a result, myoblasts can'tdifferentiate into muscle. Therefore, myostatin and activin areconsidered viable targets for muscle regeneration. However, manymyostatin and activin antagonists such as soluble activin receptor typeIIB (sActRIIB) also bind bone morphogenetic proteins (BMPs) due tocertain structural similarities. BMPs, especially, BMP-9 and BMP-10, areconsidered pivotal morphogenetic signals, orchestrating tissuearchitecture throughout the body. Inhibition of such BMPs may lead toundesired pathological conditions. As described in detail below, theexperimental data described in this example confirm that Follistatinspecifically targets myostatin and activin with high affinity and doesnot bind to non-target BMPs with meaningful affinity. Thus this exampledemonstrates that Follistatin can be a safe protein therapeutic withfewer undesired off-target effects as compared to other myostatinmodulators such as sActRIIB

Specifically, commercially available follistatins (FS315, manufacturedby R&D Systems and follistatin-Fc human chimera FS315-hFc, manufacturedby Sino Biological), and FS315-GAG3-mFc fusion proteins were used toassess binding affinity and kinetics to activin, myostatin, and BMPsusing Biacore assays. Briefly, FS315 was immobilized onto a CM5 chip,and follistatin-Fc fusion proteins were captured using human or mouseantibody capture kits (GE Healthcare). Post amine-coupling, aconcentration series of activin, myostatin, or BMPs (e.g., BMP-2, -4,-6, -7, -9, -10, and GDF-11) was added as soluble analyte at 25° C.sActRIIB-hFc was used as a control. Binding affinities (Kd) and kineticswere determined using standard methods. Exemplary results are shown inTable 3.

TABLE 3 Exemplary Binding Affinity and Kinetics Data KD values (M)Ligand FS315 FS315-hFc FS315-mFc sActRIIB-hFc BMP-2 4.4E−07 no bindingno binding no binding BMP-4 1.4E−08 NM 8.1E−08 1.3E−07 BMP-6 3.6E−109.0E−10 NM 5.7E−11 BMP-7 3.8E−08 NM NM 1.1E−09 BMP-9 no binding nobinding no binding 5.4E−11 BMP-10 1.0E−07 1.5E−07 no binding 1.0E−11GDF-11 N/A 8.2E−10 1.8E−14 3.4E−10 myostatin 1.0E−13 8.4E−14 7.3E−141.3E−12 activin 7.3E−10 1.9E−10 3.8E−14 7.0E−11 NM = not measurable dueto poor curve fit or high binding to reference chip

As shown in Table 3, follistatin (e.g., FS315 or FS315-Fc) binds targetsmyostatin and activin with high affinity but does not bind BMP-9 and -10(Kd not measurable or greater than 10⁻⁷M), while sActRIIB-Fc binds tomyostatin, activin and BMPs with similar affinity. Surprisingly andimportantly, the Fc fusion increases affinity of follistatin to primarytarget myostatin by at least 10-fold.

In addition, luciferase reporter assays were used to further determineif follistatin specifically inhibits myostatin and activin signaling(Smad 2/3 pathway) but not BMP signaling (Smad 1/5/8 pathway).Specifically, a BMP Response Element (BRE)-luciferase assay was used todetermine if follistatin can inhibit Smad 1/5/8 pathway by measuringreduction of luciferase signal (Korchynskyi et al., Identification andFunctional Characterization of Distinct Critically Important BoneMorphogenetic Protein-specific Response Elements in the Id1 Promoter,(2002), J BIOL CHEM., 277(7):4883-4891). A CAGA-luciferase assay wasused to determine if follistatin can inhibit Smad 2/3 pathway bymeasuring reduction of luciferase signal (Dennler et al., Direct bindingof Smad3 and Smad4 to critical TGFβ-inducible elements in the promoterof human plasminogen activator inhibitor-type 1 gene, (1998), EMBO J,17(11):3091-3100). Briefly, HEK293 cells were co-transfected with eitherthe BRE (BRE-Id1-luc) or CAGA-luciferase (p(CAGA)₁₂-MLP-luc vector)constructs and renilla-luciferase construct (Promega pGL4.74 [hRluc/TK])overnight. The following day, cells were treated with myostatin andactivin (for Smad 2/3 pathway induction, CAGA-luciferase reporter), orBMP-9 and BMP-10 (for Smad 1/5/8 pathway induction, BRE-luciferasereporter) with or without a concentration series of follistatin. Afteran overnight incubation, the luciferase signal was determined using thePromega Dual-Glo Assay kit, with values normalized to renilla control.In this experiment, native follistatin (R&D Systems) and follistatin Fcfusion proteins (Sino Biological FS315-hFc, FS315-GAG3-mFc) were tested.FS315-GAG3-mFc is shown below.

(SEQ ID NO: 13) GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGCKPCICTVPEVSSVFIFPPKPKDVLTITLTPKVTCVVVDISKDDPEVQFSWFVDDVEVHTAQTQPREEQFNSTFRSVSELPIMHQDWLNGKEFKCRVNSAAFPAPIEKTISKTKGRPKAPQVYTIPPPKEQMAKDKVSLTCMITDFFPEDITVEWQWNGQPAENYKNTQPIMDTDGSYFVYSKLNVQKSNWEAGNTFTCSVLHEGLHNHHTEKSL SHSPGK

Exemplary results of the BRE-luciferase assay are shown in FIG. 1.FS315-Fc does not inhibit BMP-9 or -10 signaling through the Smad 1/5/8pathway.

Exemplary results of the CAGA-luciferase assay are shown in FIG. 2. BothFS315 and FS315-GAG3-mFc showed potent inhibition of Smad2/3 signalingat doses of 0.1 nM and above as compared to the amount of Smad 2/3induction observed after administration of physiologically relevantlevels of myostatin (1.2 nM) and activin (0.4 nM), known activators ofSmad 2/3. These results indicate that follistatin is a potent andspecific inhibitor of myostatin and activin activity. The presence ofthe Fc fusion did not detrimentally affect the potency of follistatin,as indicated by the similar inhibitory curves between the native FS315molecule and the FS315-GAG3-mFc fusion protein. Unexpectedly andimportantly, the Fc fusion protein according to the present inventionsignificantly increases the binding affinity of follistatin to primarytarget myostatin (e.g., by at least 10 fold as shown in Table 3).

Example 2. Follistatin Fusion Protein FS315-GAG3-mFc has Extended SerumHalf-Life

Prior to our invention, it was reported that follistatin has a shortserum half-life, which is a concern for developing follistatin as aprotein therapeutic. For example, typical commercial FS315 protein has aserum half-life of about an hour. In this Example, the in vivo half-lifeof FS315-GAG3-mFc fusion protein was determined and it has asignificantly extended serum half-life.

Specifically, an imprinting control region (ICR) mouse was selected as amodel and I¹²⁵-labeled FS315-GAG3-mFc was administered subcutaneously at1.0 mg/kg (˜2 μCi/animal). After administration, samples of serum andtissues were taken up to 10 days post-injection. The tissues sampledwere: thyroid, liver, kidney, lung, spleen, diaphragm, heart, quadricepsand triceps. Exemplary results of the serum samples are shown in FIG.3A. As can be seen, the serum half-life of FS315-GAG3-mFc isapproximately 5 days, which is surprisingly long as compared to theshort follistatin serum half-life (about 1 hour) known in the art.Exemplary results of the PK profile across various tissues are shown inFIG. 3B and Table 4. The half-life of Follistatin-Fc, with the exceptionof the thyroid, is between two and five days across tissues. Again, theextended tissue half-life profile is unexpected.

The extended in vivo half-life data further confirm that follistatin canbe an effective protein therapeutic for treatment of DMD.

TABLE 4 Exemplary FS315-GAG3-mFc In Vivo PK Data AUC_(0-last) AUC_(0-∞)Cmax (ng/g (hr/ng/g tissue (hr/ng/g tissue tissue or or or Tissuet_(1/2) (h) ng/mL serum) ng/mL serum) ng/mL serum) Serum 134 14.0 557782 Thyroid 118 467.4 57019 71769 Kidney 77 9.8 221 249 Liver 48 4.4 118127 Lung 116 3.9 106 136 Spleen 95 5.8 72 83 Heart 105 1.6 46 55Diaphragm 99 1.0 28 33 Triceps 78 1.7 44 50 Quadriceps 99 0.8 25 31

Example 3. In Vivo Efficacy of FS315-GAG3-mFc

This Example demonstrates that administration of follistatin (e.g.,FS315-GAG3-mFc) to mdx mouse model of Duchenne muscular dystrophyresults in a trend of increased muscle mass even at a low dose of 1mg/kg. In this example, the terms “FS315-GAG3-mFc”, “FS315-Fc” and“FS315-mFc” used interchangeably.

Specifically, in this study, 45 mdx mice were treated with emptyvehicle, 0 mg/kg, 1.0 mg/kg or 8 mg/kg FS315-GAG3-mFc. Animals in thevehicle or treatment groups received two subcutaneous (interscapular)injections per week for the duration of the study and follistatin fusionprotein levels were assessed through retro-orbital sampling.

Half of the vehicle treated control animals were sacrificed with the 1mg/kg FS315-Fc group, and the remaining vehicle treated animals alongwith the untreated control animals, were sacrificed with the 8 mg/kgtreatment group. Exemplary treatment schedule was as shown in Table 5Aand B:

TABLE 5 Exemplary injection and sampling schedule in mdx Mice 5A: 1mg/kg FS315-GAG3-mFc treatment course Event Day Pre-bleed, Injection 1 0Injection 2 3 Blood sample taken, Injection 3 7 Injection 4 10 Bloodsample taken, Injection 5 14 Injection 6 17 Blood sample taken,Injection 7 21 Injection 8 24 Blood sample taken, Injection 9 29Sacrifice, week 4 time point 30 Injection 10 32 Blood sample taken,Injection 11 35 Injection 12 38 Blood sample taken 44 Injection 13 45Injection 14 49 Blood sample taken, Injection 15 52 Injection 16 56Blood sample taken, Injection 17 59 Injection 18 63 Injection 19 66Blood sample taken 70 Final sacrifice, week 10 71

5B. 8 mg/kg FS315-GAG3-mFc treatment course Event Day Pre-bleed 0Injection 1 1 Injection 2 5 Blood sample taken, Injection 3 8 Injection4 12 Blood sample taken, Injection 5 15 Injection 6 19 Injection 7 22Injection 8 26 Blood sample taken, Injection 9 30 Injection 10 33Injection 11 37 Injection 12 41 Blood sample taken 43 Final sacrifice,week 6 44

Exemplary data regarding muscle weights in the vehicle treated versus 1mg/kg FS315-Fc group are shown in FIG. 4. Specifically, FIG. 4 shows themuscle weights for the quadriceps (FIG. 4A), gastrocnemius (FIG. 4B),tibialis anterior (FIG. 4C) and triceps (FIG. 4D) in grams after 4 and10 weeks of treatment with 1 mg/kg, and 6 weeks of treatment with 8mg/kg. The muscle weight data is adjusted for baseline body weight.

Exemplary data for the circulating levels of follistatin afteradministration is shown in FIG. 5. Specifically, FIG. 5A shows thelevels of FS315-mFc in the serum of animals treated with twice weeklyinjections of 1 mg/kg, and FIG. 5B shows the levels of FS315-mFc in theserum of animals treated twice weekly with 8 mg/kg.

As is shown in FIGS. 4-5, there is a clear indication that FS315-Fcincreases muscle mass in animal models of DMD.

Example 4. In Vivo Efficacy of Recombinant Follistatin-Fc Fusion Protein

This example demonstrates that administration of a follistatin-Fc fusionprotein results in muscle hypertrophy (e.g., increased muscle mass andmyofiber diameters) in vivo.

In this study, both C57BL/10 and mdx mice were injected withFS315-GAG3-mFc directly into the gastrocnemius muscle (intramuscular,IM). Specifically, each mouse received 2 injections, one on each side,twice weekly. The left gastrocnemius received 20 μL of a 1 mg/mLsolution of FS315-GAG3-mFc for a total of 20 μg protein per injection.The right gastrocnemius received 20 μL of PBS (vehicle control).Injections occurred twice weekly for a total of 4 weeks. 24h after thefinal injection, mice were sacrificed and the gastrocnemius muscles werecarefully dissected and weighed. A group receiving the soluble activintype IIB receptor-Fc mouse chimera (sActRIIB-mFc, R&D Systems) at thesame dose was included as a positive control. In addition, untreatedmice were included as a negative control.

FIG. 6 shows significantly increased muscle mass in both C57 controlmice as well as mdx mice after twice weekly treatment with 20 μgFS315-mFc or sActRIIB-mFc. The study design and numerical datarepresented in FIG. 6 are shown in Table 6 below:

TABLE 6 Muscle Weight Test Gastroc PBS Gastroc Test-PBS Gastroc P-Strain Group N Weight (g) Weight (g) Weight (g) Value** C57 FS315- 80.17 ± 0.016 0.15 ± 0.013  0.02 ± 0.013 0.02 mFc* (0.18) (0.16) (0.024)sActRIIB- 8 0.18 ± 0.016 0.16 ± 0.02  0.019 ± 0.017 0.09 mFc (0.17)(0.16) (0.016) Untreated 5 0.16 ± 0.013  0.16 ± 0.0074 0.0032 ±0.012  >0.99 (0.15) (0.16) (0.003) mdx FS315- 10 0.19 ± 0.017 0.17 ±0.019 0.021 ± 0.013 0.005 mFc (0.18) (0.16) (0.018) sActRIIB- 8 0.21 ±0.024 0.19 ± 0.026 0.024 ± 0.017 0.04 mFc (0.2)  (0.19) (0.018)Untreated 5 0.16 ± 0.019 0.17 ± 0.023 −0.0084 ± 0.0055  0.16 (0.16)(0.17) (−0.06)  *All Follistatin constructs used in this example containa GAG3 linker. **P-values obtained from paired t-test and areBonferroni-corrected (correcting for 6 statistical tests)

Myofiber diameters were determined through digital whole slide scanningof the injected gastrocnemius muscle. Samples were fixed in 10% neutralbuffered saline, processed and embedded in paraffin, cut into 5 μmsections, and stained with Alexa fluor 488 conjugated Wheat GermAgglutinin (WGA), a method that stains muscle cell membranes. Thescanned images were analyzed using image analysis software (ImageScopeand ImagePro Plus). For each myofiber, the average diameter wasdetermined by measuring the myofiber cross section length at 2 degreeintervals, passing through the myofiber's centroid.

In accordance with FIG. 6, FIG. 15 demonstrates an increase in themyofiber diameters of gastrocnemius muscle treated with FS315-mFc. Thisincrease occurred in both the C57 (WT, FIG. 15A) and mdx mice (FIG.15B). Demonstration of the shift to larger diameters indicates that theincreased muscle weights are a consequence of muscle hypertrophy. Table7 is a summary of exemplary mean diameter changes and correspondingstatistical analysis.

TABLE 7 MEAN DIAMETER Contrast (comparison) Mean diff Standard error pWT FS315-mFc vs vehicle 12.5 0.8 <0.0001 mdx FS315-mFc vs vehicle 5.31.2 <0.0001 No injection WT vs mdx 14.6 5.8 0.04

The statistical model used was a hierarchical linear model (HLM), whichis able to account for the multiple measurements made within eachanimal. The differences between untreated and treated legs within eachstrain and treatment group are highly significant (p<0.0001, whichcorroborate the muscle weight data).

These data demonstrate that follistatin, in particular, follistatin-Fcfusion protein can effectively induce muscle growth and treat muscleatrophy associated with DMD.

Example 5. In Vivo Efficacy of Exemplary Follistatin Variants

The in vivo half-life and efficacy data based on the wild-typefollistatin FS315 protein shown in Examples 2-4 demonstrates thatfollistatin can be used as an effective protein therapy for DMD. Thisexample demonstrates that protein therapeutics can also be developedbased on follistatin variants.

Specifically, exemplary follistatin domain deletions or point mutationswere generated as described in Table 8 below and tested for their muscleregeneration efficacy using a well-established IM/AAV delivery system tofacilitate the comparison between the variants and the wild-typefollistatin.

In this study, a total of 35 C57 mice aged 3-4 weeks were used acrossseven groups. The seven groups included five mice each, with fivefollistatin variants being tested (Table 8), and wild type FS315 and anempty vector used as controls. The gene encoding for FS315 has anadditional 29 amino acids representing the signal peptide that iscleaved upon secretion from the cell. Thus, FS315 and FS344 refer to thesame wild type construct and are used interchangeably in the examplesbelow.

TABLE 8 Efficacy Screening of Exemplary Follistatin Variants VariantMutation dFSD2 Domain 2 deletion dFSD3 Domain 3 deletion FSD1/1/3 Domain2 deletion, replacement with Domain 1 Y185A Point mutant/Domain 2 L191DPoint mutant/Domain 2

The follistatin variants were administered via a single unilateralinjection into the left quadriceps and left gastrocnemius using an AAV9vector at a dose of approximately 1×10¹¹ viral particles per animal. Thefollowing endpoints were examined at 2, 4 and 6 weeks post injection:Follistatin levels in serum and urine, mouse weight, individual muscleweights (both injected and distal muscle groups), and histology (e.g.,fiber counts, size and type, etc.). The contralateral muscle served asan intra-animal comparator for this study.

As shown in FIG. 7, both the wild type FS315 and the domain 3 deletionmutant significantly increased body weight as compared to empty vectorcontrol. In particular, the tested domain 3 deleted follistatin variantincreases body weight as early as 3 weeks post-injection.

FIG. 8 shows exemplary average muscle weights of the A) gastrocnemiusand B) quadriceps on both the ipsilateral and contralateral sides twoweeks post-injection. Both wild type FS315 and the domain 3 deletionfollistatin variants showed significantly increased muscle mass on theipsilateral side by week 2 post-injection (FIG. 8). In particular,muscles injected with FS315 and dFSD3 were 60% to 70% greater in weightas compared to empty vector (FIG. 8). The dissected quad muscle that wasinjected with dFSD3 was noticeably larger than the contra-lateraluntreated muscle at week 2 (FIG. 9).

At week 4, domain 3 deleted and wild-type follistatin increased musclemass in both injected and distal muscle. See FIG. 10. As observed atweek 2, dFSD3 caused a significant hypertrophic effect at week 4, withnoticeably larger muscle mass in injected muscle compared to theuntreated side (FIG. 11). Follistatin levels in serum, determined byELISA, were similar for the wild-type and dFSD3 treated mice, andaveraged 30 ng/mL at weeks 2, 4 and 6 (data not shown).

Myofiber size was also determined in both injected and distal muscletissues at week 2, 4 and 6 post-injection using standard histologicaland immunohistochemical methods. Exemplary week 2, 4 and 6 results areshown in FIGS. 12, 13 and 14, respectively. All statistics were doneusing 1 way ANOVA with Dunnett's Multiple Comparison Test in GraphPadPrism. Error bars represent SEM.

As shown in FIG. 12, at week 2, in injected muscles, myofiberhypertrophy was observed in Quad in the FS344 (23%), dFSD3 (30%), Y185Aand L191D groups and in Gastroc in the FS344 (17%) and dFSD3 (25%)groups. In distal muscle groups, myofiber hypertrophy was observed in TAin the dFSD2 (12%) group. No hypertrophy was observed in Triceps orDiaphragm.

As shown in FIG. 13, at week 4, in injected muscles, myofiberhypertrophy was observed in Quad in the FS344 (41%), dFSD3 (50%),dFSD113 and L191D groups and in Gastroc in the FS344 (42%), dFSD2, dFSD3(73%), dFSD113, Y185A and L191D groups. In distal muscle groups,hypertrophy was observed in TA in the dFSD3 (10%) group and in Diaphragmin the FS344 (23%) and dFSD2 (29%) groups. No hypertrophy was observedin Triceps.

As shown in FIG. 14, at week 6, in injected muscles, myofiberhypertrophy was observed in Quad in the FS344 (41%), dFSD3 (30%), Y185Agroups and in Gastroc in the FS344 (90%), dFSD3 (49%), Y185A, L191Dgroups. In distal muscles, myofiber hypertrophy was observed in TA inthe FS344 (26%), dFSD3 (41%), dFSD113, Y185A, and L191D groups and inDiaphragm in the dFSD3 (35%) group. Minimal hypertrophy was observed inTriceps.

Taken together, these results indicate that protein therapeutics may bedeveloped based on follistatin variants. For example, follistatin domaindeletions or point mutations may retain or improve muscle regenerationefficacy. As shown above, domain 3 deletion can be a particularly usefulfollistatin variant for treating DMD.

Example 6. Systemic Efficacy of FS315-GAG3-mFc

As shown in Example 4, injection of FS315-mFc into the gastrocnemiusresulted in increased muscle mass versus control muscles. This exampleshows that systemic injection of FS315-mFc is also capable of inducingmuscle growth at various sites distal to the site of injection. Allfollistatin constructs used in this example contain a GAG3 linker.

A total of 20 C57BL/6 mice were used in this study with half of theanimals receiving a subcutaneous (interscapular) injection of PBS twiceper week for 8 weeks (control) and the other half receiving asubcutaneous (interscapular) injection of 10 mg/kg FS315-mFc twice perweek for 8 weeks. Animals were sacrificed 24 hours after the lastinjection and the weight of the left and right quadriceps,gastrocnemius, tibialis anterior and triceps were measured, as was totalbody weight of the animal. Table 9 below outlines the experimentaldesign for this example.

TABLE 9 Experimental Design Sacrifice (24 hours Mouse Test InjectionDosing post last Group N Strain Article Route Dose Schedule injection) A10 WT C57BL/6 FS315- SC 10 Twice 4 weeks mFc (Interscapular) mg/kgweekly B 10 WT C57BL/6 FS315- SC 10 Twice 8 weeks mFc (Interscapular)mg/kg weekly C 10 WT C57BL/6 Vehicle SC NA Twice 4 weeks (PBS)(Interscapular) weekly D 10 WT C57BL/6 Vehicle SC NA Twice 8 weeks (PBS)(Interscapular) weekly

FIG. 16 shows exemplary body weight data through the 8 week course ofthe study. As can be seen, body weights for the FS315-mFc treatedanimals were significantly greater than those vehicle treated controlanimals beginning at 2 weeks and continuing throughout the 8 week study.FIG. 17 represents exemplary muscle weight data. The triceps musclesfrom mice treated with FS315-mFc were significantly greater in weightcompared to vehicle control as early as week 4. After 8 weeks oftreatment, both triceps and quadriceps muscle groups demonstratedsignificant increases in weight compare to vehicle (FIG. 17). Myofibersize was determined by the method described in Example 4. FIG. 18 showsthe percent increase in myofiber diameter for the triceps and quadricepsmuscle groups at weeks 4 and 8. Both muscle groups demonstrated a shifttowards greater myofiber size after treatment with FS315-mFc at both 4and 8 weeks.

In addition, serum follistatin levels were increased followingsubcutaneous injection. For example, FS315-mFc levels in the sera oftreated mice (by twice weekly subcutaneous injection) are shown in FIG.19. FS315-mFc levels were highest in the serum collected at weeks 4 and8 sacrifice time points, consistent with the amount of time between theFS315-mFc injection and the serum collection (24h). At these points,serum levels of FS315-mFc averaged about 200 ng/mL. The biweeklyretro-orbital bleeds were collected 3 days after FS315-mFc injection,and serum levels of FS315-mFc averaged between about 30-50 ng/mL.

These data demonstrates that systemic injection of FS315-mFc (e.g.,subcutaneous injection) can effectively induce muscle growth in variousmuscle tissues throughout the body.

Example 7. Systemic Efficacy of Follistatin-Fc Fusion Protein in DMDMouse Model

This example further demonstrates systemic efficacy in DMD diseasemodel. In particular, as shown below, systemic injection of FS315-mFcsuccessfully reduced progression of various characteristic DMD symptomssuch as muscle necrosis and/or fibrosis. All follistatin constructs usedin this example contain a GAG3 linker.

The mdx mouse model has been used extensively as the preclinical modelfor demonstrating proof of concept of candidate therapies for DMD. Boththe limb muscle groups and diaphragm of the mdx mouse show extensivepathology that tends to increase with age. Such pathology ischaracterized by areas of inflammatory infiltrate, necrosis, andfibrosis in muscle. FS315-mFc was tested in this model to evaluate itseffect on progression of fibrosis in muscle. A total of 50 mdx mice wereused in this Example, with 20 animals receiving a subcutaneous injectionof PBS, and 30 animals receiving a subcutaneous injection of 10 mg/kgFS315-mFc twice per week for 12 weeks. (see Table 10). Animals weresacrificed 24 hours after the last injection and tissues were collectedfor analysis of necrosis and fibrosis (see Table 11).

TABLE 10 Experimental Design Sacrifice (24 hours Test Injection Dosingpost last Group N Article Route Dose Schedule injection) A 15 FS315- SC10 Twice  6 weeks mFc mg/kg weekly B 10 PBS SC N/A Twice  6 weeks weeklyC 15 FS315- SC 10 Twice 12 weeks mFc mg/kg weekly D 10 PBS SC N/A Twice12 weeks weekly

TABLE 11 Tissue collection and processing Diaphragm QuadricepsGastrocnemius Triceps ½ snap frozen for 1 snap frozen for 1 snap frozenfor 1 snap frozen for protein analysis protein analysis protein analysisprotein analysis ½ fixed in formalin 1 fixed in formalin for 1 fixed informalin for 1 fixed in formalin for for histological histologicalanalysis histological analysis histological analysis analysis

FIG. 20 shows exemplary effect of FS315-mFc on fibrotic proteinexpression at the RNA level. Specifically, RT-PCR of collagen type I,alpha-smooth muscle actin, and collagen triple helix repeat containing 1protein demonstrated a significant reduction in the expression of thesefibrosis-related proteins as early as 6 weeks after twice weekly SCtreatment.

Tables 12 and 13 summarize the histopathological evaluation of necrosis(as determined by evaluation of H&E stained sections) and fibrosis (asdetermined by evaluation of collagen I stained muscle sections inFS315-mFc treated mdx mouse muscle) in muscle tissue sections. For theFS315-mFc and vehicle treated groups, there were 15 and 10 total animalsper group, respectively. As indicated in Table 12, FS315-mFc treatmentsignificantly reduced the incidence of necrosis in limb muscles as earlyas 6 weeks from initiation of twice weekly injections. This reduction innecrosis is illustrated in the images of H&E sections through quadricepsand triceps muscle (FIG. 21). The incidence of fibrosis, demonstrated bycollagen I staining of muscle tissue sections, was significantly reducedafter 12 weeks of FS315-mFc treatment (also see Table 13). Thisreduction in collagen deposition is illustrated in the images ofcollagen I stained muscle sections (FIG. 22).

The results of this study demonstrates that FS315-mFc can successfullytreat DMD by effectively reducing the progression of the diseased musclepathology in the DMD mouse model including, but not limited to, musclenecrosis and/or fibrosis

TABLE 12 Incidence of necrosis in FS315-mFc treated mdx mouse muscle (pvalues indicate degree of significance between vehicle and FS315-mFc,using Fisher's Exact Test) Score Vehicle FS315-mFc Vehicle FS315-mFcWeek 6 Quad p = 0.001 Week 12 Quad p = 0.049 Minimal 10% 67% 30% 73%Mild 40% 33% 70% 27% Marked 50% 0% 0% 0% Week 6 Triceps p < 0.001 Week12 Triceps p = 0.02 Minimal 0% 53% 20% 73% Mild 10% 33% 70% 20% Marked90% 14% 10% 7% Week 6 Gastroc p < 0.001 Week 12 Gastroc p = 0.007Minimal 0% 73% 20% 80% Mild 40% 27% 60% 20% Marked 60% 0% 20% 0%Minimal: <5%; mild: <30%; marked: >30% in total checked muscle area

TABLE 13 Incidence of fibrosis, (p values indicate degree ofsignificance between vehicle and FS315-mFc, using Fisher's Exact Test)Score Vehicle FS315-mFc Week 12 Quad p = 0.0001 Minimal 0% 80% Mild 70%20% Marked 30% 0% Week 12 Triceps p = 0.001 Minimal 0% 67% Mild 80% 20%Marked 20% 13% Week 12 Gastroc p < 0.0001 Minimal 0% 73% Mild 20% 27%Marked 80% 0% Minimal: ~1%; mild: <5%; marked: >5% in total checkedmuscle area

Example 8. In Vivo Efficacy of Recombinant Follistatin Domain 3 DeletionFc Fusion Protein

This Example demonstrates that a follistatin domain 3 deletion (dFSD3)Fc fusion protein effectively induced muscle growth in vivo, similar towild type follistatin-Fc fusion protein. All follistatin constructs usedin this example contain a GAG3 linker.

Specifically, the domain 3 deleted construct described in Example 5 wasfused to the same mFc as used for FS315-mFc. In addition, the same GAG3linker sequence was used to fuse dFSD3 to mFc. C57BL/10 mice wereinjected with both fusion proteins directly into the gastrocnemiusmuscle, as described in Example 4. Mice were sacrificed after 4 weeks oftwice weekly injections of 20 μg of fusion protein, and the oppositegastrocnemius muscle received the same volume of PBS. 24h after thefinal injection, the treated mice were sacrificed and the injectedgastrocnemius muscles were carefully injected and weighed. As indicatedin FIG. 23, the dFSD3-GAG3-mFc fusion protein led to a significantincrease in muscle mass over vehicle control, and the increase wassimilar to that observed with FS315-mFc. This Example indicates that afollistatin domain 3 deletion Fc fusion protein (e.g., dFSD3-GAG3-mFc)is active in vivo and another promising therapeutic candidate for DMDtreatment.

Example 9. Advantage of Longer Linker on Follistatin Function

This example demonstrates that a longer linker, in particular a linkercontaining at least 10 amino acids, provides unexpected advantage onfollistatin function. Specifically, this example shows that theFS315-GAG3-Fc fusion protein (murine and/or human Fc), containing a 57amino acid linker, is more potent in its ability to inhibit myostatinand activin compared to a commercial available FS315-hFc fusion proteinfrom Sino Biological (Sino Biological Inc. Catalog Number 10685-H02H),which contains a 9 amino acid linker ALEVLFQGP (SEQ ID NO: 18). Theconcentration of myostatin and activin used for the signaling assay was1.2 nM. As indicated in FIG. 24 and Table 14, the FS315-GAG3-mFc andFS315-GAG3-hFc fusion proteins inhibit myostatin and activin signalingin the CAGA-luciferase assay to the same extent as native FS315. Incomparison, the commercially available FS315-hFc fusion protein (SinoBiological) is significantly less potent. The calculated IC50's are asfollows:

TABLE 14 Exemplary IC50 values for follistatin inhibition of myostatinand activin in the CAGA-luciferase reporter assay for Smad2/3 signalingMaterial Ligand IC50 (nM) FS315 (R&D Systems) Myostatin 0.45FS315-GAG3-mFc Myostatin 0.46 FS315-GAG3-hFc Myostatin 0.68 FS315-hFc(Sino Biological) Myostatin 2.99 FS315 (R&D Systems) Activin 0.40FS315-GAG3-mFc Activin 0.36 FS315-GAG3-hFc Activin 0.70 FS315-hFc (SinoBiological) Activin 2.90

Without wishing to be held to a particular theory, it is possible that alonger linker (e.g., a 57 amino acid linker in this particular constructFS315-GAG3-Fc) between the FS315 protein and the Fc region may permit amore native conformation of FS315 as compared to a fusion protein with amuch shorter linker (e.g., 9 amino acids), allowing for binding totarget ligands and inhibition of signaling to a similar extent as thatobserved with native FS315. In comparison, the commercially availableFS315-hFc protein has a much shorter linker of 9 amino acids, withsignificantly less separation between the Fc and the FS315 protein,potentially causing a detrimental effect on FS315 conformation andphysiological activity.

Example 10. Follistatin Fusion Protein FS315-GAG3-hFc has Extended SerumHalf-Life

In this example, we demonstrated that provided follistatin fusionproteins, in particular, those with a longer linker (e.g., a linker withat least 10 amino acids) has extended serum half-life. Specifically, forthe first time, we demonstrated here a FS315 fused to human Fc with theGAG3 linker (FS315-GAG3-hFc), has an extended serum half-life whenadministered subcutaneously (SC) into Sprague-Dawley rats at a singledose of 10 mg/kg. After administration, serum was collected at timepoints ranging from 15 min to 5 days. FS315-GAG3-hFc was measured in ratserum using a Mesoscale Discovery (MSD) assay that captures the humanFS315 and detects the human Fc domain of the intact fusion protein inserum samples. Levels of FS315-GAG3-hFc in rat serum are shown in FIG.25. The PK parameters are summarized in Table 15.

TABLE 15 FS315-GAG3-hFc In Vivo PK Data AUC0-last AUC0-∞ t ½ (h) Cmax(ng/mL) Tmax (h) (hr * ng/mL) (hr * ng/mL) 84 1372 48 114585 205803

In sum, the above Examples demonstrate that follistatin, includingprovided variants, are highly effective in inducing muscle hypertrophyand attenuating muscle necrosis and fibrosis in DMD disease model by,e.g., systemic administration. Thus, follistatin and provided variantscan be effective protein therapeutics for the treatment of DMD.

EQUIVALENTS AND SCOPE

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. The scope of the presentinvention is not intended to be limited to the above Description, butrather is as set forth in the following claims.

I claim:
 1. A method of treating Duchenne muscular dystrophy (DMD)comprising administering to an individual who is suffering from orsusceptible to DMD an effective amount of a recombinant follistatinprotein comprising an amino acid sequence of SEQ ID NO: 1 or 2 fused toan Fc domain via a peptide linker comprising 10 or more amino acids suchthat at least one symptom or feature of DMD is reduced in intensity,severity, or frequency, or has delayed onset, and wherein the peptidelinker comprises the amino acid sequence of SEQ ID NO: 5, 6, or
 7. 2.The method of claim 1, wherein the recombinant follistatin proteincomprises a deletion of amino acids residues 212-288 of SEQ ID NO:1. 3.The method of claim 1, wherein the Fc domain comprises an amino acidsequence of (SEQ ID NO: 3)EPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK.


4. The method of claim 1, wherein the recombinant follistatin protein isproduced from mammalian cells.
 5. The method of claim 1, wherein therecombinant follistatin protein is administered systemically.
 6. Themethod of claim 1, wherein the administration of the recombinantfollistatin protein results in muscle regeneration, increased musclestrength, increased flexibility, increased range of motion, increasedstamina, reduced fatigability, increased blood flow, improved cognition,improved pulmonary function, inflammation inhibition, reduced musclefibrosis, and/or reduced muscle necrosis.
 7. The method of claim 1,wherein the at least one symptom or feature of DMD is selected from thegroup consisting of muscle wasting, muscle weakness, muscle fragility,muscle necrosis, muscle fibrosis, joint contracture, skeletaldeformation, cardiomyopathy, impaired swallowing, impaired bowel andbladder function, muscle ischemia, cognitive impairment, behavioraldysfunction, socialization impairment, scoliosis, and impairedrespiratory function.
 8. A recombinant follistatin fusion proteincomprising a follistatin polypeptide; an Fc domain; and a linker thatassociates the follistatin polypeptide with the Fc domain, wherein thefollistatin polypeptide comprises an amino acid sequence of SEQ ID NO.:1 or 2; wherein the linker comprises the amino acid sequence of SEQ IDNO: 5, 6, or 7; and further wherein the recombinant follistatin fusionprotein is capable of binding to activin, myostatin and/or GDF-11 andhas an in vivo half-life ranging from about 0.5-10 days.
 9. Therecombinant follistatin fusion protein of claim 8, wherein thefollistatin polypeptide contains a deletion of amino acids residues212-288 of SEQ ID NO:1.
 10. The recombinant follistatin fusion proteinof claim 8, wherein the Fc domain is an IgG1 Fc domain.
 11. Therecombinant follistatin fusion protein of claim 8, wherein the Fc domainhas an amino acid sequence of (SEQ ID NO: 3)EPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK.


12. The recombinant follistatin fusion protein of claim 8, wherein therecombinant follistatin fusion protein comprises an amino acid sequenceof SEQ ID NO: 8 GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 8), or SEQ ID NO: 9GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCIKAKSCEDIQCTGGKKCLWDFKVGRGRCSLCDELCPDSKSDEPVCASDNATYASECAMKEAACSSGVLLEVKHSGSCNSISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 9).


13. The recombinant follistatin fusion protein of claim 8, wherein therecombinant follistatin fusion protein comprises an amino acid sequenceof SEQ ID NO: 10 GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCISISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 10), or SEQ ID NO: 11GNCWLRQAKNGRCQVLYKTELSKEECCSTGRLSTSWTEEDVNDNTLFKWMIFNGGAPNCIPCKETCENVDCGPGKKCRMNKKNKPRCVCAPDCSNITWKGPVCGLDGKTYRNECALLKARCKEQPELEVQYQGRCKKTCRDVFCPGSSTCVVDQTNNAYCVTCNRICPEPASSEQYLCGNDGVTYSSACHLRKATCLLGRSIGLAYEGKCISISEDTEEEEEDEDQDYSFPISSILEWGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPGGGGGAAAAAGGGGGGAPEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 11).


14. A nucleic acid comprising a nucleotide sequence encoding therecombinant follistatin fusion protein of claim
 8. 15. A cell comprisinga nucleic acid of claim
 14. 16. A pharmaceutical composition comprisinga recombinant follistatin fusion protein of claim 8 and apharmaceutically acceptable carrier.
 17. A method of treating Duchennemuscular dystrophy (DMD) comprising administering to an individual whois suffering from or susceptible to DMD an effective amount of arecombinant follistatin protein comprising an amino acid sequence SEQ IDNOs: 8, 9, 10 or 11, such that at least one symptom or feature of DMD isreduced in intensity, severity, or frequency, or has delayed onset.